diff --git a/backend-node/src/controllers/departmentController.ts b/backend-node/src/controllers/departmentController.ts
index 93b37475..9e3f0b6a 100644
--- a/backend-node/src/controllers/departmentController.ts
+++ b/backend-node/src/controllers/departmentController.ts
@@ -250,25 +250,19 @@ export async function deleteDepartment(req: AuthenticatedRequest, res: Response)
     if (parseInt(hasChildren?.count || "0") > 0) {
       res.status(400).json({
         success: false,
-        message: "하위 부서가 있는 부서는 삭제할 수 없습니다.",
+        message: "하위 부서가 있는 부서는 삭제할 수 없습니다. 먼저 하위 부서를 삭제해주세요.",
       });
       return;
     }
 
-    // 부서원 확인
-    const hasMembers = await queryOne<any>(`
-      SELECT COUNT(*) as count
-      FROM user_dept
+    // 부서원 삭제 (부서 삭제 전에 먼저 삭제)
+    const deletedMembers = await query<any>(`
+      DELETE FROM user_dept
       WHERE dept_code = $1
+      RETURNING user_id
     `, [deptCode]);
 
-    if (parseInt(hasMembers?.count || "0") > 0) {
-      res.status(400).json({
-        success: false,
-        message: "부서원이 있는 부서는 삭제할 수 없습니다.",
-      });
-      return;
-    }
+    const memberCount = deletedMembers.length;
 
     // 부서 삭제
     const result = await query<any>(`
@@ -285,11 +279,17 @@ export async function deleteDepartment(req: AuthenticatedRequest, res: Response)
       return;
     }
 
-    logger.info("부서 삭제 성공", { deptCode });
+    logger.info("부서 삭제 성공", { 
+      deptCode, 
+      deptName: result[0].dept_name,
+      deletedMemberCount: memberCount 
+    });
 
     res.status(200).json({
       success: true,
-      message: "부서가 삭제되었습니다.",
+      message: memberCount > 0 
+        ? `부서가 삭제되었습니다. (부서원 ${memberCount}명 제외됨)` 
+        : "부서가 삭제되었습니다.",
     });
   } catch (error) {
     logger.error("부서 삭제 실패", error);
diff --git a/frontend/components/admin/department/DepartmentMembers.tsx b/frontend/components/admin/department/DepartmentMembers.tsx
index 6fb398ec..7147971b 100644
--- a/frontend/components/admin/department/DepartmentMembers.tsx
+++ b/frontend/components/admin/department/DepartmentMembers.tsx
@@ -13,6 +13,7 @@ import {
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { Badge } from "@/components/ui/badge";
+import { useToast } from "@/hooks/use-toast";
 import type { Department, DepartmentMember } from "@/types/department";
 import * as departmentAPI from "@/lib/api/department";
 
@@ -30,6 +31,7 @@ export function DepartmentMembers({
   selectedDepartment,
   onMemberChange,
 }: DepartmentMembersProps) {
+  const { toast } = useToast();
   const [members, setMembers] = useState<DepartmentMember[]>([]);
   const [isLoading, setIsLoading] = useState(false);
   const [isAddModalOpen, setIsAddModalOpen] = useState(false);
@@ -108,16 +110,31 @@ export function DepartmentMembers({
         setSearchResults([]);
         loadMembers();
         onMemberChange?.(); // 부서 구조 새로고침
+        
+        // 성공 Toast 표시
+        toast({
+          title: "부서원 추가 완료",
+          description: "부서원이 추가되었습니다.",
+          variant: "default",
+        });
       } else {
         if ((response as any).isDuplicate) {
           setDuplicateMessage(response.error || "이미 해당 부서의 부서원입니다.");
         } else {
-          alert(response.error || "부서원 추가에 실패했습니다.");
+          toast({
+            title: "부서원 추가 실패",
+            description: response.error || "부서원 추가에 실패했습니다.",
+            variant: "destructive",
+          });
         }
       }
     } catch (error) {
       console.error("부서원 추가 실패:", error);
-      alert("부서원 추가 중 오류가 발생했습니다.");
+      toast({
+        title: "부서원 추가 실패",
+        description: "부서원 추가 중 오류가 발생했습니다.",
+        variant: "destructive",
+      });
     }
   };
 
@@ -142,12 +159,27 @@ export function DepartmentMembers({
         setMemberToRemove(null);
         loadMembers();
         onMemberChange?.(); // 부서 구조 새로고침
+        
+        // 성공 Toast 표시
+        toast({
+          title: "부서원 제거 완료",
+          description: `${memberToRemove.name} 님이 부서에서 제외되었습니다.`,
+          variant: "default",
+        });
       } else {
-        alert(response.error || "부서원 제거에 실패했습니다.");
+        toast({
+          title: "부서원 제거 실패",
+          description: response.error || "부서원 제거에 실패했습니다.",
+          variant: "destructive",
+        });
       }
     } catch (error) {
       console.error("부서원 제거 실패:", error);
-      alert("부서원 제거 중 오류가 발생했습니다.");
+      toast({
+        title: "부서원 제거 실패",
+        description: "부서원 제거 중 오류가 발생했습니다.",
+        variant: "destructive",
+      });
     }
   };
 
@@ -163,12 +195,27 @@ export function DepartmentMembers({
 
       if (response.success) {
         loadMembers();
+        
+        // 성공 Toast 표시
+        toast({
+          title: "주 부서 설정 완료",
+          description: "주 부서가 변경되었습니다.",
+          variant: "default",
+        });
       } else {
-        alert(response.error || "주 부서 설정에 실패했습니다.");
+        toast({
+          title: "주 부서 설정 실패",
+          description: response.error || "주 부서 설정에 실패했습니다.",
+          variant: "destructive",
+        });
       }
     } catch (error) {
       console.error("주 부서 설정 실패:", error);
-      alert("주 부서 설정 중 오류가 발생했습니다.");
+      toast({
+        title: "주 부서 설정 실패",
+        description: "주 부서 설정 중 오류가 발생했습니다.",
+        variant: "destructive",
+      });
     }
   };
 
diff --git a/frontend/components/admin/department/DepartmentStructure.tsx b/frontend/components/admin/department/DepartmentStructure.tsx
index 49df54bc..4347d612 100644
--- a/frontend/components/admin/department/DepartmentStructure.tsx
+++ b/frontend/components/admin/department/DepartmentStructure.tsx
@@ -3,16 +3,11 @@
 import { useState, useEffect } from "react";
 import { Plus, ChevronDown, ChevronRight, Users, Trash2 } from "lucide-react";
 import { Button } from "@/components/ui/button";
-import {
-  Dialog,
-  DialogContent,
-  DialogHeader,
-  DialogTitle,
-  DialogFooter,
-} from "@/components/ui/dialog";
+import { Dialog, DialogContent, DialogHeader, DialogTitle, DialogFooter } from "@/components/ui/dialog";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import type { Department, DepartmentFormData } from "@/types/department";
+import { useToast } from "@/hooks/use-toast";
+import type { Department } from "@/types/department";
 import * as departmentAPI from "@/lib/api/department";
 
 interface DepartmentStructureProps {
@@ -31,6 +26,7 @@ export function DepartmentStructure({
   onSelectDepartment,
   refreshTrigger,
 }: DepartmentStructureProps) {
+  const { toast } = useToast();
   const [departments, setDepartments] = useState<Department[]>([]);
   const [expandedDepts, setExpandedDepts] = useState<Set<string>>(new Set());
   const [isLoading, setIsLoading] = useState(false);
@@ -40,10 +36,11 @@ export function DepartmentStructure({
   const [parentDeptForAdd, setParentDeptForAdd] = useState<string | null>(null);
   const [newDeptName, setNewDeptName] = useState("");
   const [duplicateMessage, setDuplicateMessage] = useState<string | null>(null);
-  
+
   // 부서 삭제 확인 모달
   const [deleteConfirmOpen, setDeleteConfirmOpen] = useState(false);
   const [deptToDelete, setDeptToDelete] = useState<{ code: string; name: string } | null>(null);
+  const [deleteErrorMessage, setDeleteErrorMessage] = useState<string | null>(null);
 
   // 부서 목록 로드
   useEffect(() => {
@@ -97,16 +94,31 @@ export function DepartmentStructure({
         setNewDeptName("");
         setParentDeptForAdd(null);
         loadDepartments();
+
+        // 성공 Toast 표시
+        toast({
+          title: "부서 생성 완료",
+          description: `"${newDeptName}" 부서가 생성되었습니다.`,
+          variant: "default",
+        });
       } else {
         if ((response as any).isDuplicate) {
           setDuplicateMessage(response.error || "이미 존재하는 부서명입니다.");
         } else {
-          alert(response.error || "부서 추가에 실패했습니다.");
+          toast({
+            title: "부서 생성 실패",
+            description: response.error || "부서 추가에 실패했습니다.",
+            variant: "destructive",
+          });
         }
       }
     } catch (error) {
       console.error("부서 추가 실패:", error);
-      alert("부서 추가 중 오류가 발생했습니다.");
+      toast({
+        title: "부서 생성 실패",
+        description: "부서 추가 중 오류가 발생했습니다.",
+        variant: "destructive",
+      });
     }
   };
 
@@ -124,15 +136,32 @@ export function DepartmentStructure({
       const response = await departmentAPI.deleteDepartment(deptToDelete.code);
 
       if (response.success) {
+        // 삭제된 부서가 선택되어 있었다면 선택 해제
+        if (selectedDepartment?.dept_code === deptToDelete.code) {
+          onSelectDepartment(null);
+        }
+
         setDeleteConfirmOpen(false);
         setDeptToDelete(null);
         loadDepartments();
+
+        // 성공 메시지 Toast로 표시 (부서원 수 포함)
+        toast({
+          title: "부서 삭제 완료",
+          description: response.message || "부서가 삭제되었습니다.",
+          variant: "default",
+        });
       } else {
-        alert(response.error || "부서 삭제에 실패했습니다.");
+        // 삭제 확인 모달을 닫고 에러 모달을 표시
+        setDeleteConfirmOpen(false);
+        setDeptToDelete(null);
+        setDeleteErrorMessage(response.error || "부서 삭제에 실패했습니다.");
       }
     } catch (error) {
       console.error("부서 삭제 실패:", error);
-      alert("부서 삭제 중 오류가 발생했습니다.");
+      setDeleteConfirmOpen(false);
+      setDeptToDelete(null);
+      setDeleteErrorMessage("부서 삭제 중 오류가 발생했습니다.");
     }
   };
 
@@ -160,15 +189,12 @@ export function DepartmentStructure({
         <div key={dept.dept_code}>
           {/* 부서 항목 */}
           <div
-            className={`flex cursor-pointer items-center justify-between rounded-lg p-2 text-sm transition-colors hover:bg-muted ${
+            className={`hover:bg-muted flex cursor-pointer items-center justify-between rounded-lg p-2 text-sm transition-colors ${
               isSelected ? "bg-primary/10 text-primary" : ""
             }`}
             style={{ marginLeft: `${level * 16}px` }}
           >
-            <div
-              className="flex flex-1 items-center gap-2"
-              onClick={() => onSelectDepartment(dept)}
-            >
+            <div className="flex flex-1 items-center gap-2" onClick={() => onSelectDepartment(dept)}>
               {/* 확장/축소 아이콘 */}
               {hasChildren ? (
                 <button
@@ -178,11 +204,7 @@ export function DepartmentStructure({
                   }}
                   className="h-4 w-4"
                 >
-                  {isExpanded ? (
-                    <ChevronDown className="h-4 w-4" />
-                  ) : (
-                    <ChevronRight className="h-4 w-4" />
-                  )}
+                  {isExpanded ? <ChevronDown className="h-4 w-4" /> : <ChevronRight className="h-4 w-4" />}
                 </button>
               ) : (
                 <div className="h-4 w-4" />
@@ -192,7 +214,7 @@ export function DepartmentStructure({
               <span className="font-medium">{dept.dept_name}</span>
 
               {/* 인원수 */}
-              <div className="flex items-center gap-1 text-xs text-muted-foreground">
+              <div className="text-muted-foreground flex items-center gap-1 text-xs">
                 <Users className="h-3 w-3" />
                 <span>{dept.memberCount || 0}</span>
               </div>
@@ -214,7 +236,7 @@ export function DepartmentStructure({
               <Button
                 variant="ghost"
                 size="icon"
-                className="h-6 w-6 text-destructive"
+                className="text-destructive h-6 w-6"
                 onClick={(e) => {
                   e.stopPropagation();
                   handleDeleteDepartmentRequest(dept.dept_code, dept.dept_name);
@@ -244,11 +266,11 @@ export function DepartmentStructure({
       </div>
 
       {/* 부서 트리 */}
-      <div className="space-y-1 rounded-lg border bg-card p-4 shadow-sm">
+      <div className="bg-card space-y-1 rounded-lg border p-4 shadow-sm">
         {isLoading ? (
-          <div className="py-8 text-center text-sm text-muted-foreground">로딩 중...</div>
+          <div className="text-muted-foreground py-8 text-center text-sm">로딩 중...</div>
         ) : departments.length === 0 ? (
-          <div className="py-8 text-center text-sm text-muted-foreground">
+          <div className="text-muted-foreground py-8 text-center text-sm">
             부서가 없습니다. 최상위 부서를 추가해주세요.
           </div>
         ) : (
@@ -260,9 +282,7 @@ export function DepartmentStructure({
       <Dialog open={isAddModalOpen} onOpenChange={setIsAddModalOpen}>
         <DialogContent className="sm:max-w-[425px]">
           <DialogHeader>
-            <DialogTitle>
-              {parentDeptForAdd ? "하위 부서 추가" : "최상위 부서 추가"}
-            </DialogTitle>
+            <DialogTitle>{parentDeptForAdd ? "하위 부서 추가" : "최상위 부서 추가"}</DialogTitle>
           </DialogHeader>
 
           <div className="space-y-4 py-4">
@@ -301,10 +321,7 @@ export function DepartmentStructure({
             <p className="text-sm">{duplicateMessage}</p>
           </div>
           <DialogFooter>
-            <Button
-              onClick={() => setDuplicateMessage(null)}
-              className="h-8 text-xs sm:h-10 sm:text-sm"
-            >
+            <Button onClick={() => setDuplicateMessage(null)} className="h-8 text-xs sm:h-10 sm:text-sm">
               확인
             </Button>
           </DialogFooter>
@@ -321,9 +338,7 @@ export function DepartmentStructure({
             <p className="text-sm">
               <span className="font-semibold">{deptToDelete?.name}</span> 부서를 삭제하시겠습니까?
             </p>
-            <p className="mt-2 text-xs text-muted-foreground">
-              이 작업은 되돌릴 수 없습니다.
-            </p>
+            <p className="text-muted-foreground mt-2 text-xs">이 작업은 되돌릴 수 없습니다.</p>
           </div>
           <DialogFooter className="gap-2 sm:gap-0">
             <Button
@@ -346,7 +361,23 @@ export function DepartmentStructure({
           </DialogFooter>
         </DialogContent>
       </Dialog>
+
+      {/* 부서 삭제 에러 모달 */}
+      <Dialog open={!!deleteErrorMessage} onOpenChange={() => setDeleteErrorMessage(null)}>
+        <DialogContent className="max-w-[95vw] sm:max-w-[400px]">
+          <DialogHeader>
+            <DialogTitle className="text-base sm:text-lg">삭제 불가</DialogTitle>
+          </DialogHeader>
+          <div className="py-4">
+            <p className="text-sm">{deleteErrorMessage}</p>
+          </div>
+          <DialogFooter>
+            <Button onClick={() => setDeleteErrorMessage(null)} className="h-8 text-xs sm:h-10 sm:text-sm">
+              확인
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
     </div>
   );
 }
-