diff --git a/src/wp-admin/includes/class-wp-posts-list-table.php b/src/wp-admin/includes/class-wp-posts-list-table.php
index bc25dd0045a87..a1f4a5ea7eea8 100644
--- a/src/wp-admin/includes/class-wp-posts-list-table.php
+++ b/src/wp-admin/includes/class-wp-posts-list-table.php
@@ -1781,7 +1781,7 @@ public function inline_edit() {
 					<div class="inline-edit-group wp-clearfix">
 						<label class="alignleft">
 							<span class="title"><?php _e( 'Password' ); ?></span>
-							<span class="input-text-wrap"><input type="text" name="post_password" class="inline-edit-password-input" value="" /></span>
+							<span class="input-text-wrap"><input type="text" name="post_password" class="inline-edit-password-input" value="" maxlength="255" /></span>
 						</label>
 
 						<span class="alignleft inline-edit-or">
diff --git a/src/wp-admin/includes/post.php b/src/wp-admin/includes/post.php
index ebdd61df345dc..ca88e537bd2a1 100644
--- a/src/wp-admin/includes/post.php
+++ b/src/wp-admin/includes/post.php
@@ -156,6 +156,10 @@ function _wp_translate_postdata( $update = false, $post_data = null ) {
 		unset( $post_data['post_password'] );
 	}
 
+	if ( isset( $post_data['post_password'] ) && strlen( $post_data['post_password'] ) > 255 ) {
+		return new WP_Error( 'invalid_post_password_length', __( 'Post passwords cannot be longer than 255 characters.' ) );
+	}
+
 	if ( ! isset( $post_data['comment_status'] ) ) {
 		$post_data['comment_status'] = 'closed';
 	}
diff --git a/tests/phpunit/tests/admin/includesPost.php b/tests/phpunit/tests/admin/includesPost.php
index de7b42f5eb15a..0cde7b8745104 100644
--- a/tests/phpunit/tests/admin/includesPost.php
+++ b/tests/phpunit/tests/admin/includesPost.php
@@ -26,6 +26,9 @@ public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ) {
 		self::$post_id = $factory->post->create();
 	}
 
+	/**
+	 * @covers ::_wp_translate_postdata
+	*/
 	public function test__wp_translate_postdata_cap_checks_contributor() {
 		wp_set_current_user( self::$contributor_id );
 
@@ -1325,4 +1328,55 @@ public function test_user_get_refreshed_metabox_nonce() {
 		$this->assertNotEmpty( $response['wp-refresh-metabox-loader-nonces']['replace']['_wpnonce'] );
 		$this->assertNotEmpty( $response['wp-refresh-metabox-loader-nonces']['replace']['metabox_loader_nonce'] );
 	}
+
+	/**
+	 * Test that _wp_translate_postdata() validates post password length.
+	 *
+	 * @ticket 63943
+	 * @covers ::_wp_translate_postdata
+	 */
+	public function test_validity_post_password_length() {
+		wp_set_current_user( self::$editor_id );
+
+		// Test valid password within 255 character limit.
+		$valid_password = str_repeat( 'a', 255 );
+		$post_data      = array(
+			'post_type'     => 'post',
+			'post_password' => $valid_password,
+		);
+
+		$result = _wp_translate_postdata( false, $post_data );
+		$this->assertNotWPError( $result );
+		$this->assertSame( $valid_password, $result['post_password'] );
+
+		// Test password over 255 characters should fail.
+		$invalid_password = str_repeat( 'a', 256 );
+		$post_data        = array(
+			'post_type'     => 'post',
+			'post_password' => $invalid_password,
+		);
+
+		$result = _wp_translate_postdata( false, $post_data );
+		$this->assertWPError( $result );
+		$this->assertSame( 'invalid_post_password_length', $result->get_error_code() );
+	}
+
+	/**
+	 * Test that _wp_translate_postdata() removes post password for users without publish_posts capability.
+	 *
+	 * @covers ::_wp_translate_postdata
+	 */
+	public function test_post_password_removed_for_users_without_publish_posts_cap() {
+		wp_set_current_user( self::$contributor_id );
+
+		// Contributors cannot publish posts, so password should be removed.
+		$post_data = array(
+			'post_type'     => 'post',
+			'post_password' => 'test_password',
+			'post_status'   => 'draft',
+		);
+
+		$result = _wp_translate_postdata( false, $post_data );
+		$this->assertArrayNotHasKey( 'post_password', $result );
+	}
 }