תשתמש בinnerHTML :
HTML קוד:
<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
function changeit(){
document.getElementById('bla').innerHTML='';
}
//-->
</script>
</head>
<body>
<div id="bla" onmouseover="changeit()">asdasd</div>
</body>
</html>