Add  element to node body field via WYSIWYG
TinyMCE outputs HTML 4.01 Transitional markup by default, and  is not allowed inside  in that (or XHTML) because styles are not block elements.

You can however force TinyMCE to accept [the invalid] style elements inside the body by overriding the valid_children setting.

/**
 * Implements hook_wysiwyg_editor_settings_alter().
 */
function MYMODULE_wysiwyg_editor_settings_alter(&amp;$settings, $context) {
  if ($context['profile']-&gt;editor == 'tinymce') {
    $settings['valid_children'] = '+body[style]';
  }
}


Thanks to TwoD for supplying the answer.