More Information

Page template in subdirectory

If the page template is located in a subdirectory of the theme (since WP 3.4), prepend the folder name and a slash to the template filename, e.g.:

is_page_template( 'templates/about.php' );

Cannot Be Used Inside The Loop

Due to certain global variables being overwritten during The Loop is_page_template() will not work. In order to use it after The Loop you must call wp_reset_query() after The Loop.

Alternative

Since the page template slug is stored inside the post_meta for any post that has been assigned to a page template, it is possible to directly query the post_meta to see whether any given page has been assigned a page template. This is the method that is_page_template() uses internally.

The function get_page_template_slug( $post_id ) will return the slug of the currently assigned page template (or an empty string if no template has been assigned – or false if the $post_id does not correspond to an actual page). You can easily use this anywhere (in The Loop, or outside) to determine whether any page has been assigned a page template.

  // in the loop:
  if ( get_page_template_slug( get_the_ID() ) ){
     // Yep, this page has a page template
  }

  // anywhere:
  if ( get_page_template_slug( $some_post_ID ) ){
     // Uh-huh.
  }