diff --git a/README.md b/README.md
index 1b871b0..b247654 100644
--- a/README.md
+++ b/README.md
@@ -227,6 +227,7 @@ function useMcp(options: UseMcpOptions): UseMcpResult
 | `autoReconnect` | `boolean \| number` | Auto reconnect if an established connection is lost, with delay in ms (default: 3000) |
 | `transportType` | `'auto' \| 'http' \| 'sse'` | Transport type preference: 'auto' (HTTP with SSE fallback), 'http' (HTTP only), 'sse' (SSE only) (default: 'auto') |
 | `preventAutoAuth` | `boolean` | Prevent automatic authentication popup on initial connection (default: false) |
+| `onPopupWindow` | `(url: string, features: string, window: Window \| null) => void` | Callback invoked just after the authentication popup window is opened |
 
 #### Return Value
 
diff --git a/src/auth/browser-provider.ts b/src/auth/browser-provider.ts
index 7b0e7b1..04c708c 100644
--- a/src/auth/browser-provider.ts
+++ b/src/auth/browser-provider.ts
@@ -15,6 +15,7 @@ export class BrowserOAuthClientProvider implements OAuthClientProvider {
   readonly clientName: string
   readonly clientUri: string
   readonly callbackUrl: string
+  readonly onPopupWindow: ((url: string, features: string, window: Window | null) => void) | undefined
 
   constructor(
     serverUrl: string,
@@ -23,6 +24,7 @@ export class BrowserOAuthClientProvider implements OAuthClientProvider {
       clientName?: string
       clientUri?: string
       callbackUrl?: string
+      onPopupWindow?: (url: string, features: string, window: Window | null) => void
     } = {},
   ) {
     this.serverUrl = serverUrl
@@ -34,6 +36,7 @@ export class BrowserOAuthClientProvider implements OAuthClientProvider {
       options.callbackUrl ||
         (typeof window !== 'undefined' ? new URL('/oauth/callback', window.location.origin).toString() : '/oauth/callback'),
     )
+    this.onPopupWindow = options.onPopupWindow
   }
 
   // --- SDK Interface Methods ---
@@ -169,6 +172,11 @@ export class BrowserOAuthClientProvider implements OAuthClientProvider {
     try {
       const popup = window.open(sanitizedAuthUrl, `mcp_auth_${this.serverUrlHash}`, popupFeatures)
 
+      // If a callback is provided, invoke it after opening the popup
+      if (this.onPopupWindow) {
+        this.onPopupWindow(sanitizedAuthUrl, popupFeatures, popup)
+      }
+
       if (!popup || popup.closed || typeof popup.closed === 'undefined') {
         console.warn(
           `[${this.storageKeyPrefix}] Popup likely blocked by browser. Manual navigation might be required using the stored URL.`,
diff --git a/src/react/types.ts b/src/react/types.ts
index 61934ea..b80df54 100644
--- a/src/react/types.ts
+++ b/src/react/types.ts
@@ -30,6 +30,12 @@ export type UseMcpOptions = {
   transportType?: 'auto' | 'http' | 'sse'
   /** Prevent automatic authentication popup on initial connection (default: false) */
   preventAutoAuth?: boolean
+  /**
+   * Callback function that is invoked just before the authentication popup window is opened.
+   * @param url The URL that will be opened in the popup.
+   * @param features The features string for the popup window.
+   */
+  onPopupWindow?: (url: string, features: string, window: Window | null) => void
 }
 
 export type UseMcpResult = {
diff --git a/src/react/useMcp.ts b/src/react/useMcp.ts
index f95b4f2..c7239f1 100644
--- a/src/react/useMcp.ts
+++ b/src/react/useMcp.ts
@@ -47,6 +47,7 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
     autoReconnect = DEFAULT_RECONNECT_DELAY,
     transportType = 'auto',
     preventAutoAuth = false,
+    onPopupWindow,
   } = options
 
   const [state, setState] = useState<UseMcpResult['state']>('discovering')
@@ -176,6 +177,7 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
         clientName,
         clientUri,
         callbackUrl,
+        onPopupWindow,
       })
       addLog('debug', 'BrowserOAuthClientProvider initialized in connect.')
     }
@@ -779,6 +781,7 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
         clientName,
         clientUri,
         callbackUrl,
+        onPopupWindow,
       })
       addLog('debug', 'BrowserOAuthClientProvider initialized/updated on mount/option change.')
     }