diff --git a/adminfront/src/features/tenants/routes/TenantAdminsAndOwnersTab.tsx b/adminfront/src/features/tenants/routes/TenantAdminsAndOwnersTab.tsx
index 4031f590..da160f0f 100644
--- a/adminfront/src/features/tenants/routes/TenantAdminsAndOwnersTab.tsx
+++ b/adminfront/src/features/tenants/routes/TenantAdminsAndOwnersTab.tsx
@@ -82,14 +82,35 @@ export function TenantAdminsAndOwnersTab() {
 
   const addOwnerMutation = useMutation({
     mutationFn: (userId: string) => addTenantOwner(tenantId, userId),
+    onMutate: async (userId) => {
+      await queryClient.cancelQueries({ queryKey: ["tenant-owners", tenantId] });
+      const previousOwners = queryClient.getQueryData<any[]>(["tenant-owners", tenantId]);
+      
+      // Optimistically add to the list to prevent immediate double clicks
+      const addedUser = searchResults.find(u => u.id === userId);
+      if (addedUser) {
+        queryClient.setQueryData<any[]>(["tenant-owners", tenantId], old => {
+          if (!old) return [{ id: userId, name: addedUser.name, email: addedUser.email }];
+          if (old.some(o => o.id === userId)) return old;
+          return [...old, { id: userId, name: addedUser.name, email: addedUser.email }];
+        });
+      }
+      return { previousOwners };
+    },
     onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ["tenant-owners", tenantId] });
+      // Delay invalidation slightly to give the backend outbox time to process
+      setTimeout(() => {
+        queryClient.invalidateQueries({ queryKey: ["tenant-owners", tenantId] });
+      }, 1000);
       toast.success(
         t("msg.admin.tenants.owners.add_success", "소유자가 추가되었습니다."),
       );
       setSearchTerm("");
     },
-    onError: (err: AxiosError<{ error?: string }>) => {
+    onError: (err: AxiosError<{ error?: string }>, userId, context) => {
+      if (context?.previousOwners) {
+        queryClient.setQueryData(["tenant-owners", tenantId], context.previousOwners);
+      }
       toast.error(
         err.response?.data?.error ||
           t("msg.common.error", "오류가 발생했습니다."),
@@ -99,8 +120,18 @@ export function TenantAdminsAndOwnersTab() {
 
   const removeOwnerMutation = useMutation({
     mutationFn: (userId: string) => removeTenantOwner(tenantId, userId),
+    onMutate: async (userId) => {
+      await queryClient.cancelQueries({ queryKey: ["tenant-owners", tenantId] });
+      const previousOwners = queryClient.getQueryData<any[]>(["tenant-owners", tenantId]);
+      queryClient.setQueryData<any[]>(["tenant-owners", tenantId], old => 
+        old ? old.filter(o => o.id !== userId) : []
+      );
+      return { previousOwners };
+    },
     onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ["tenant-owners", tenantId] });
+      setTimeout(() => {
+        queryClient.invalidateQueries({ queryKey: ["tenant-owners", tenantId] });
+      }, 1000);
       toast.success(
         t(
           "msg.admin.tenants.owners.remove_success",
@@ -108,7 +139,10 @@ export function TenantAdminsAndOwnersTab() {
         ),
       );
     },
-    onError: (err: AxiosError<{ error?: string }>) => {
+    onError: (err: AxiosError<{ error?: string }>, userId, context) => {
+      if (context?.previousOwners) {
+        queryClient.setQueryData(["tenant-owners", tenantId], context.previousOwners);
+      }
       toast.error(
         err.response?.data?.error ||
           t("msg.common.error", "오류가 발생했습니다."),
@@ -118,14 +152,33 @@ export function TenantAdminsAndOwnersTab() {
 
   const addAdminMutation = useMutation({
     mutationFn: (userId: string) => addTenantAdmin(tenantId, userId),
+    onMutate: async (userId) => {
+      await queryClient.cancelQueries({ queryKey: ["tenant-admins", tenantId] });
+      const previousAdmins = queryClient.getQueryData<any[]>(["tenant-admins", tenantId]);
+      
+      const addedUser = searchResults.find(u => u.id === userId);
+      if (addedUser) {
+        queryClient.setQueryData<any[]>(["tenant-admins", tenantId], old => {
+          if (!old) return [{ id: userId, name: addedUser.name, email: addedUser.email }];
+          if (old.some(a => a.id === userId)) return old;
+          return [...old, { id: userId, name: addedUser.name, email: addedUser.email }];
+        });
+      }
+      return { previousAdmins };
+    },
     onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ["tenant-admins", tenantId] });
+      setTimeout(() => {
+        queryClient.invalidateQueries({ queryKey: ["tenant-admins", tenantId] });
+      }, 1000);
       toast.success(
         t("msg.admin.tenants.admins.add_success", "관리자가 추가되었습니다."),
       );
       setSearchTerm("");
     },
-    onError: (err: AxiosError<{ error?: string }>) => {
+    onError: (err: AxiosError<{ error?: string }>, userId, context) => {
+      if (context?.previousAdmins) {
+        queryClient.setQueryData(["tenant-admins", tenantId], context.previousAdmins);
+      }
       toast.error(
         err.response?.data?.error ||
           t("msg.common.error", "오류가 발생했습니다."),
@@ -135,13 +188,26 @@ export function TenantAdminsAndOwnersTab() {
 
   const removeAdminMutation = useMutation({
     mutationFn: (userId: string) => removeTenantAdmin(tenantId, userId),
+    onMutate: async (userId) => {
+      await queryClient.cancelQueries({ queryKey: ["tenant-admins", tenantId] });
+      const previousAdmins = queryClient.getQueryData<any[]>(["tenant-admins", tenantId]);
+      queryClient.setQueryData<any[]>(["tenant-admins", tenantId], old => 
+        old ? old.filter(a => a.id !== userId) : []
+      );
+      return { previousAdmins };
+    },
     onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ["tenant-admins", tenantId] });
+      setTimeout(() => {
+        queryClient.invalidateQueries({ queryKey: ["tenant-admins", tenantId] });
+      }, 1000);
       toast.success(
         t("msg.admin.tenants.admins.remove_success", "권한이 회수되었습니다."),
       );
     },
-    onError: (err: AxiosError<{ error?: string }>) => {
+    onError: (err: AxiosError<{ error?: string }>, userId, context) => {
+      if (context?.previousAdmins) {
+        queryClient.setQueryData(["tenant-admins", tenantId], context.previousAdmins);
+      }
       toast.error(
         err.response?.data?.error ||
           t("msg.common.error", "오류가 발생했습니다."),
diff --git a/backend/internal/handler/tenant_handler.go b/backend/internal/handler/tenant_handler.go
index a9b9c28d..a6fa095e 100644
--- a/backend/internal/handler/tenant_handler.go
+++ b/backend/internal/handler/tenant_handler.go
@@ -529,6 +529,13 @@ func (h *TenantHandler) AddAdmin(c *fiber.Ctx) error {
 		return errorJSON(c, fiber.StatusBadRequest, "tenantId and userId are required")
 	}
 
+	if h.Keto != nil {
+		relations, err := h.Keto.ListRelations(c.Context(), "Tenant", tenantID, "admins", "User:"+userID)
+		if err == nil && len(relations) > 0 {
+			return errorJSON(c, fiber.StatusConflict, "이미 관리자로 등록된 사용자입니다.")
+		}
+	}
+
 	if h.KetoOutbox != nil {
 		_ = h.KetoOutbox.Create(c.Context(), &domain.KetoOutbox{
 			Namespace: "Tenant",
@@ -660,6 +667,13 @@ func (h *TenantHandler) AddOwner(c *fiber.Ctx) error {
 		return errorJSON(c, fiber.StatusBadRequest, "tenantId and userId are required")
 	}
 
+	if h.Keto != nil {
+		relations, err := h.Keto.ListRelations(c.Context(), "Tenant", tenantID, "owners", "User:"+userID)
+		if err == nil && len(relations) > 0 {
+			return errorJSON(c, fiber.StatusConflict, "이미 소유자로 등록된 사용자입니다.")
+		}
+	}
+
 	if h.KetoOutbox != nil {
 		_ = h.KetoOutbox.Create(c.Context(), &domain.KetoOutbox{
 			Namespace: "Tenant",