diff --git a/.env.example b/.env.example
index 1734305..efef8c1 100644
--- a/.env.example
+++ b/.env.example
@@ -12,6 +12,10 @@ BETTER_AUTH_SECRET=replace-with-at-least-32-random-bytes
 # Separate trusted browser origins with commas for local development or proxies.
 BETTER_AUTH_TRUSTED_ORIGINS=http://localhost:3000
 
+# Cloudflare Turnstile administrator login protection
+TURNSTILE_SITE_KEY=replace-with-turnstile-site-key
+TURNSTILE_SECRET_KEY=replace-with-turnstile-secret-key
+
 # Redis remote cache, event transport, and outbox worker
 REDIS_URL=rediss://default:replace-me@redis.example.internal:6379
 REDIS_CACHE_PREFIX=buzz:next-cache
diff --git a/app/admin/login/page.tsx b/app/admin/login/page.tsx
index 05bc6ac..943b8be 100644
--- a/app/admin/login/page.tsx
+++ b/app/admin/login/page.tsx
@@ -9,11 +9,16 @@ export default async function AdminLoginPage() {
   await connection();
   if (await getAdminSession()) redirect("/admin");
 
+  const turnstileSiteKey = process.env.TURNSTILE_SITE_KEY;
+  if (!turnstileSiteKey) {
+    throw new Error("TURNSTILE_SITE_KEY is required for administrator login.");
+  }
+
   return (
     <div className="min-h-svh">
       <SiteHeader />
       <main className="grid min-h-[calc(100svh-4rem)] place-items-center px-4 py-12">
-        <LoginCard />
+        <LoginCard turnstileSiteKey={turnstileSiteKey} />
       </main>
     </div>
   );
diff --git a/components/admin/login-card.tsx b/components/admin/login-card.tsx
index 2bdb6f6..b26f7d0 100644
--- a/components/admin/login-card.tsx
+++ b/components/admin/login-card.tsx
@@ -3,7 +3,8 @@
 import { CircleAlertIcon, LogInIcon } from "lucide-react";
 import Link from "next/link";
 import { useRouter } from "next/navigation";
-import { type FormEvent, useState } from "react";
+import Script from "next/script";
+import { type FormEvent, useCallback, useRef, useState } from "react";
 
 import {
   Alert,
@@ -24,13 +25,73 @@ import { Input } from "@/components/ui/input";
 import { Spinner } from "@/components/ui/spinner";
 import { authClient } from "@/lib/auth/client";
 
-export function LoginCard() {
+interface TurnstileApi {
+  render(
+    container: HTMLElement,
+    options: {
+      sitekey: string;
+      callback: (token: string) => void;
+      "expired-callback": () => void;
+      "error-callback": () => void;
+    },
+  ): string;
+  reset(widgetId: string): void;
+}
+
+declare global {
+  interface Window {
+    turnstile?: TurnstileApi;
+  }
+}
+
+interface LoginCardProps {
+  turnstileSiteKey: string;
+}
+
+export function LoginCard({ turnstileSiteKey }: LoginCardProps) {
   const router = useRouter();
+  const turnstileContainerRef = useRef<HTMLDivElement>(null);
+  const turnstileWidgetIdRef = useRef<string | null>(null);
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  const [turnstileToken, setTurnstileToken] = useState<string | null>(null);
+
+  const renderTurnstile = useCallback(() => {
+    if (
+      !window.turnstile ||
+      !turnstileContainerRef.current ||
+      turnstileWidgetIdRef.current
+    ) {
+      return;
+    }
+
+    turnstileWidgetIdRef.current = window.turnstile.render(
+      turnstileContainerRef.current,
+      {
+        sitekey: turnstileSiteKey,
+        callback: (token) => {
+          setTurnstileToken(token);
+          setError(null);
+        },
+        "expired-callback": () => setTurnstileToken(null),
+        "error-callback": () => {
+          setTurnstileToken(null);
+          setError("ยืนยันตัวตนไม่สำเร็จ โปรดลองอีกครั้ง");
+        },
+      },
+    );
+  }, [turnstileSiteKey]);
+
+  function resetTurnstile() {
+    setTurnstileToken(null);
+    if (window.turnstile && turnstileWidgetIdRef.current) {
+      window.turnstile.reset(turnstileWidgetIdRef.current);
+    }
+  }
 
   async function signIn(event: FormEvent<HTMLFormElement>) {
     event.preventDefault();
+    if (!turnstileToken) return;
     setLoading(true);
     setError(null);
 
@@ -43,6 +104,9 @@ export function LoginCard() {
         email,
         password,
         rememberMe: true,
+        fetchOptions: {
+          headers: { "x-captcha-response": turnstileToken },
+        },
       });
       if (result.error) {
         setError(
@@ -57,6 +121,7 @@ export function LoginCard() {
     } catch {
       setError("เชื่อมต่อระบบเข้าสู่ระบบไม่ได้ โปรดลองอีกครั้ง");
     } finally {
+      resetTurnstile();
       setLoading(false);
     }
   }
@@ -96,6 +161,19 @@ export function LoginCard() {
                 required
               />
             </Field>
+            <Field>
+              <div ref={turnstileContainerRef} className="min-h-[65px]" />
+              <Script
+                src="https://challenges.cloudflare.com/turnstile/v0/api.js?render=explicit"
+                strategy="afterInteractive"
+                onLoad={renderTurnstile}
+                onReady={renderTurnstile}
+                onError={() => {
+                  setTurnstileToken(null);
+                  setError("โหลดระบบยืนยันตัวตนไม่สำเร็จ โปรดลองอีกครั้ง");
+                }}
+              />
+            </Field>
             {error ? (
               <Alert variant="destructive">
                 <CircleAlertIcon aria-hidden="true" />
@@ -103,7 +181,12 @@ export function LoginCard() {
                 <AlertDescription>{error}</AlertDescription>
               </Alert>
             ) : null}
-            <Button className="w-full" size="lg" type="submit" disabled={loading}>
+            <Button
+              className="w-full"
+              size="lg"
+              type="submit"
+              disabled={loading || !turnstileToken}
+            >
               {loading ? (
                 <Spinner data-icon="inline-start" />
               ) : (
diff --git a/lib/auth/server.ts b/lib/auth/server.ts
index 1f8b5fa..b85833a 100644
--- a/lib/auth/server.ts
+++ b/lib/auth/server.ts
@@ -3,7 +3,7 @@ import "server-only";
 import { betterAuth } from "better-auth";
 import { drizzleAdapter } from "better-auth/adapters/drizzle";
 import { nextCookies } from "better-auth/next-js";
-import { admin } from "better-auth/plugins";
+import { admin, captcha } from "better-auth/plugins";
 import { headers } from "next/headers";
 
 import { getDb } from "@/db";
@@ -60,7 +60,15 @@ function createAuth() {
         },
       },
     },
-    plugins: [admin({ defaultRole: "admin" }), nextCookies()],
+    plugins: [
+      captcha({
+        provider: "cloudflare-turnstile",
+        secretKey: required("TURNSTILE_SECRET_KEY"),
+        endpoints: ["/sign-in/email"],
+      }),
+      admin({ defaultRole: "admin" }),
+      nextCookies(),
+    ],
   });
 }
 
diff --git a/tests/security-boundaries.test.ts b/tests/security-boundaries.test.ts
index fc79a1e..08ae6d3 100644
--- a/tests/security-boundaries.test.ts
+++ b/tests/security-boundaries.test.ts
@@ -33,4 +33,25 @@ describe("administrative security boundaries", () => {
       source.lastIndexOf("getAdminSession"),
     );
   });
+
+  it("enforces Cloudflare Turnstile on email sign-in", async () => {
+    const source = await readFile(
+      new URL("../lib/auth/server.ts", import.meta.url),
+      "utf8",
+    );
+    expect(source).toContain('provider: "cloudflare-turnstile"');
+    expect(source).toContain('secretKey: required("TURNSTILE_SECRET_KEY")');
+    expect(source).toContain('endpoints: ["/sign-in/email"]');
+  });
+
+  it("requires a Turnstile token before submitting administrator login", async () => {
+    const source = await readFile(
+      new URL("../components/admin/login-card.tsx", import.meta.url),
+      "utf8",
+    );
+    expect(source).toContain('headers: { "x-captcha-response": turnstileToken }');
+    expect(source).toContain("disabled={loading || !turnstileToken}");
+    expect(source).toContain('"expired-callback": () => setTurnstileToken(null)');
+    expect(source).toContain("resetTurnstile();");
+  });
 });