How can I serve a separate CSS file for Internet Explorer? I am setting responsive design for only IE (Internet Explorer) in Drupal 7.

Is there any method or solution this file is working with only IE not for Firefox and Chrome?
Use drupal_add_css with the option 'browsers'.

drupal_add_css(
  path_to_theme() . '/ie.css',
  array(
    'browsers' =&gt; array(
      'IE' =&gt; 'lte IE 9',
      '!IE' =&gt; FALSE
    )
  )
);


You should add this function call in your theme's template.php file through template_preprocess_html like this:

function MYTHEME_preprocess_html(&amp;$vars){
  drupal_add_css(
      path_to_theme() . '/css/ie.css',
      array(
        'browsers' =&gt; array(
          'IE' =&gt; 'lte IE 9',
          '!IE' =&gt; FALSE
        )
      )
    );
}