WordPress v3.5 introduces the filter xmlrpc_enabled:
add_filter('xmlrpc_enabled', '__return_false');
You can add this code to your wp_config.php after the line require_once(ABSPATH . 'wp-settings.php'); if you want to disable XML-RPC for your site.
from
here
Also, there are a few plugins in the plugin repository that do this for you or block access to it. Try that option.