Its possible using jquery.
Try this
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="
http://www.w3.org/1999/xhtml"
>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Untitled Document</title>
<script type="text/javascript" src="jquery-1.4.2.min.js">
</script>
<script language="javascript">
function fadeIframe()
{
$("#iframe1").fadeOut("slo
w");
}
</script>
</head>
<body>
<iframe src="
http://google.com" width="400" height="500" id="iframe1" ></iframe>
<!--
-->
<input value="Fade" type="button" onclick="fadeIframe()" />
</body>
</html>
Full working code attached.