use this code:
put this code in head section
<script type="text/javascript">
function print(divid)
{
var prtContent = document.getElementById(strid);
var WinPrint;
WinPrint.document.write(prtContent.innerHTML);
WinPrint.document.close();
WinPrint.focus();
WinPrint.print();
prtContent.innerHTML=strOldOne;
}
</script>
and put this code on body tag
call javascript function on aspbutton "OnClientClick" Event