diff --git a/packages/api/src/admin/roles.spec.ts b/packages/api/src/admin/roles.spec.ts
index 5fe7fda091..3015345d69 100644
--- a/packages/api/src/admin/roles.spec.ts
+++ b/packages/api/src/admin/roles.spec.ts
@@ -1086,6 +1086,42 @@ describe('createAdminRolesHandlers', () => {
       expect(deps.updateUser).not.toHaveBeenCalled();
     });
 
+    it('returns 400 when removing the last admin user', async () => {
+      const deps = createDeps({
+        getRoleByName: jest.fn().mockResolvedValue(mockRole({ name: SystemRoles.ADMIN })),
+        findUser: jest.fn().mockResolvedValue(mockUser({ role: SystemRoles.ADMIN })),
+        countUsersByRole: jest.fn().mockResolvedValue(1),
+      });
+      const handlers = createAdminRolesHandlers(deps);
+      const { req, res, status, json } = createReqRes({
+        params: { name: SystemRoles.ADMIN, userId: validUserId },
+      });
+
+      await handlers.removeRoleMember(req, res);
+
+      expect(status).toHaveBeenCalledWith(400);
+      expect(json).toHaveBeenCalledWith({ error: 'Cannot remove the last admin user' });
+      expect(deps.updateUser).not.toHaveBeenCalled();
+    });
+
+    it('allows removing an admin when multiple admins exist', async () => {
+      const deps = createDeps({
+        getRoleByName: jest.fn().mockResolvedValue(mockRole({ name: SystemRoles.ADMIN })),
+        findUser: jest.fn().mockResolvedValue(mockUser({ role: SystemRoles.ADMIN })),
+        countUsersByRole: jest.fn().mockResolvedValue(3),
+      });
+      const handlers = createAdminRolesHandlers(deps);
+      const { req, res, status, json } = createReqRes({
+        params: { name: SystemRoles.ADMIN, userId: validUserId },
+      });
+
+      await handlers.removeRoleMember(req, res);
+
+      expect(status).toHaveBeenCalledWith(200);
+      expect(json).toHaveBeenCalledWith({ success: true });
+      expect(deps.updateUser).toHaveBeenCalledWith(validUserId, { role: SystemRoles.USER });
+    });
+
     it('returns 500 on unexpected error', async () => {
       const deps = createDeps({
         getRoleByName: jest.fn().mockResolvedValue(mockRole()),
diff --git a/packages/api/src/admin/roles.ts b/packages/api/src/admin/roles.ts
index 0477d9a7d7..753c481d9f 100644
--- a/packages/api/src/admin/roles.ts
+++ b/packages/api/src/admin/roles.ts
@@ -337,6 +337,13 @@ export function createAdminRolesHandlers(deps: AdminRolesDeps) {
         return res.status(400).json({ error: 'User is not a member of this role' });
       }
 
+      if (name === SystemRoles.ADMIN) {
+        const adminCount = await countUsersByRole(SystemRoles.ADMIN);
+        if (adminCount <= 1) {
+          return res.status(400).json({ error: 'Cannot remove the last admin user' });
+        }
+      }
+
       await updateUser(userId, { role: SystemRoles.USER });
       return res.status(200).json({ success: true });
     } catch (error) {