diff --git a/client/src/components/OAuthCallback.tsx b/client/src/components/OAuthCallback.tsx
index 80ed62bb7..9c19e6957 100644
--- a/client/src/components/OAuthCallback.tsx
+++ b/client/src/components/OAuthCallback.tsx
@@ -36,6 +36,9 @@ const OAuthCallback = ({ onConnect }: OAuthCallbackProps) => {
         });
 
       const params = parseOAuthCallbackParams(window.location.search);
+      // Extract state from query params
+      const urlParams = new URLSearchParams(window.location.search);
+      const returnedState = urlParams.get("state");
       if (!params.successful) {
         return notifyError(generateOAuthErrorDescription(params));
       }
@@ -45,6 +48,20 @@ const OAuthCallback = ({ onConnect }: OAuthCallbackProps) => {
         return notifyError("Missing Server URL");
       }
 
+      // Validate state parameter
+      const serverAuthProvider = new InspectorOAuthClientProvider(
+        serverUrl,
+        undefined,
+        undefined,
+      );
+      const expectedState = serverAuthProvider.getState();
+      serverAuthProvider.clearState(); // Always clear after checking
+      if (!returnedState || !expectedState || returnedState !== expectedState) {
+        return notifyError(
+          "Invalid or missing OAuth state parameter. Please try logging in again.",
+        );
+      }
+
       const clientInformation =
         await getClientInformationFromSessionStorage(serverUrl);
 
diff --git a/client/src/components/__tests__/Sidebar.test.tsx b/client/src/components/__tests__/Sidebar.test.tsx
index 980dc0120..ad7c2125b 100644
--- a/client/src/components/__tests__/Sidebar.test.tsx
+++ b/client/src/components/__tests__/Sidebar.test.tsx
@@ -27,6 +27,10 @@ describe("Sidebar Environment Variables", () => {
     setEnv: jest.fn(),
     bearerToken: "",
     setBearerToken: jest.fn(),
+    oauthClientId: "",
+    setOauthClientId: jest.fn(),
+    oauthParams: "",
+    setOauthParams: jest.fn(),
     onConnect: jest.fn(),
     onDisconnect: jest.fn(),
     stdErrNotifications: [],
diff --git a/client/src/lib/auth.authorize-url.test.ts b/client/src/lib/auth.authorize-url.test.ts
new file mode 100644
index 000000000..53c6404db
--- /dev/null
+++ b/client/src/lib/auth.authorize-url.test.ts
@@ -0,0 +1,45 @@
+import { InspectorOAuthClientProvider } from "./auth";
+
+describe("OAuth /authorize URL includes state parameter", () => {
+  const serverUrl = "https://example.com";
+  let provider: InspectorOAuthClientProvider;
+
+  // Suppress console.log for this test suite
+  beforeAll(() => {
+    jest.spyOn(console, "log").mockImplementation(() => {});
+  });
+
+  beforeEach(() => {
+    provider = new InspectorOAuthClientProvider(serverUrl);
+    sessionStorage.clear();
+  });
+
+  it("includes state parameter in the authorization URL", () => {
+    // Mock window.location.href using Object.defineProperty
+    const originalLocation = window.location;
+
+    Object.defineProperty(window, "location", {
+      value: { href: "" },
+      writable: true,
+    });
+
+    const url = new URL("https://authserver.com/authorize");
+    provider.redirectToAuthorization(url);
+
+    // Check that the URL contains the state parameter
+    expect(window.location.href).toContain("state=");
+    const stateInUrl = new URL(window.location.href).searchParams.get("state");
+    expect(stateInUrl).toBeDefined();
+    expect(stateInUrl!.length).toBeGreaterThan(0);
+
+    // Restore window.location
+    Object.defineProperty(window, "location", {
+      value: originalLocation,
+      writable: true,
+    });
+  });
+
+  afterAll(() => {
+    (console.log as jest.Mock).mockRestore();
+  });
+});
diff --git a/client/src/lib/auth.state.test.ts b/client/src/lib/auth.state.test.ts
new file mode 100644
index 000000000..6aa3fd3ae
--- /dev/null
+++ b/client/src/lib/auth.state.test.ts
@@ -0,0 +1,31 @@
+import { InspectorOAuthClientProvider } from "./auth";
+
+describe("InspectorOAuthClientProvider state parameter", () => {
+  const serverUrl = "https://example.com";
+  let provider: InspectorOAuthClientProvider;
+
+  beforeEach(() => {
+    provider = new InspectorOAuthClientProvider(serverUrl);
+    sessionStorage.clear();
+  });
+
+  it("generates, stores, and retrieves state", () => {
+    const state = provider.generateAndStoreState();
+    expect(state).toBeDefined();
+    expect(state).toEqual(provider.getState());
+    expect(state).toHaveLength(32);
+  });
+
+  it("clears state from sessionStorage", () => {
+    provider.generateAndStoreState();
+    provider.clearState();
+    expect(provider.getState()).toBeNull();
+  });
+
+  it("generates a new state each time", () => {
+    const state1 = provider.generateAndStoreState();
+    provider.clearState();
+    const state2 = provider.generateAndStoreState();
+    expect(state1).not.toEqual(state2);
+  });
+});
diff --git a/client/src/lib/auth.ts b/client/src/lib/auth.ts
index 8d034296a..a41340c28 100644
--- a/client/src/lib/auth.ts
+++ b/client/src/lib/auth.ts
@@ -6,6 +6,7 @@ import {
   OAuthTokensSchema,
 } from "@modelcontextprotocol/sdk/shared/auth.js";
 import { SESSION_KEYS, getServerSpecificKey } from "./constants";
+import { generateRandomState } from "@/utils/oauthUtils";
 
 export const getClientInformationFromSessionStorage = async (
   serverUrl: string,
@@ -98,7 +99,36 @@ export class InspectorOAuthClientProvider implements OAuthClientProvider {
     sessionStorage.setItem(key, JSON.stringify(tokens));
   }
 
+  /**
+   * Generate, store, and return a new state parameter for OAuth.
+   */
+  generateAndStoreState(): string {
+    const state = generateRandomState(32);
+    const key = getServerSpecificKey(SESSION_KEYS.OAUTH_STATE, this.serverUrl);
+    sessionStorage.setItem(key, state);
+    return state;
+  }
+
+  /**
+   * Retrieve the stored state parameter for this serverUrl.
+   */
+  getState(): string | null {
+    const key = getServerSpecificKey(SESSION_KEYS.OAUTH_STATE, this.serverUrl);
+    return sessionStorage.getItem(key);
+  }
+
+  /**
+   * Remove the stored state parameter for this serverUrl.
+   */
+  clearState() {
+    const key = getServerSpecificKey(SESSION_KEYS.OAUTH_STATE, this.serverUrl);
+    sessionStorage.removeItem(key);
+  }
+
   redirectToAuthorization(authorizationUrl: URL) {
+    // Generate and store a new state parameter
+    const state = this.generateAndStoreState();
+    authorizationUrl.searchParams.set("state", state);
     const authParams = this.authParams();
     console.log("authParams", authParams);
     if (authParams) {
diff --git a/client/src/lib/constants.ts b/client/src/lib/constants.ts
index d1d3e0787..b574250ae 100644
--- a/client/src/lib/constants.ts
+++ b/client/src/lib/constants.ts
@@ -7,6 +7,7 @@ export const SESSION_KEYS = {
   TOKENS: "mcp_tokens",
   CLIENT_INFORMATION: "mcp_client_information",
   OAUTH_PARAMS: "mcp_oauth_params",
+  OAUTH_STATE: "oauth_state",
 } as const;
 
 // Generate server-specific session storage keys
diff --git a/client/src/utils/__tests__/oauthUtils.ts b/client/src/utils/__tests__/oauthUtils.ts
index cc9674cb2..22e3757fe 100644
--- a/client/src/utils/__tests__/oauthUtils.ts
+++ b/client/src/utils/__tests__/oauthUtils.ts
@@ -1,7 +1,8 @@
 import {
   generateOAuthErrorDescription,
   parseOAuthCallbackParams,
-} from "@/utils/oauthUtils.ts";
+  generateRandomState,
+} from "@/utils/oauthUtils";
 
 describe("parseOAuthCallbackParams", () => {
   it("Returns successful: true and code when present", () => {
@@ -76,3 +77,27 @@ describe("generateOAuthErrorDescription", () => {
     );
   });
 });
+
+describe("generateRandomState", () => {
+  it("generates a string of the correct length", () => {
+    const state = generateRandomState(32);
+    expect(state).toHaveLength(32);
+    const state16 = generateRandomState(16);
+    expect(state16).toHaveLength(16);
+  });
+
+  it("generates a string with only allowed characters", () => {
+    const charset =
+      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+    const state = generateRandomState(64);
+    for (const char of state) {
+      expect(charset.includes(char)).toBe(true);
+    }
+  });
+
+  it("generates different values on subsequent calls (randomness)", () => {
+    const state1 = generateRandomState(32);
+    const state2 = generateRandomState(32);
+    expect(state1).not.toEqual(state2);
+  });
+});
diff --git a/client/src/utils/oauthUtils.ts b/client/src/utils/oauthUtils.ts
index c971271e3..db9ba22ff 100644
--- a/client/src/utils/oauthUtils.ts
+++ b/client/src/utils/oauthUtils.ts
@@ -63,3 +63,15 @@ export const generateOAuthErrorDescription = (
     .filter(Boolean)
     .join("\n");
 };
+
+/**
+ * Generates a cryptographically secure random string for use as OAuth state or PKCE code_verifier.
+ * @param length Number of characters in the generated string (default: 32)
+ */
+export function generateRandomState(length = 32): string {
+  const charset =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+  const array = new Uint8Array(length);
+  window.crypto.getRandomValues(array);
+  return Array.from(array, (byte) => charset[byte % charset.length]).join("");
+}