You need to remove the option from DropDownList.
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script type="text/javascript">
window.onload = function () {
var select = document.getElementById("<%=ddlFruits.ClientID %>");
select.removeChild(select.options[0]);
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="ddlFruits" runat="server">
<asp:ListItem Text="Mango" Value="Mango" />
<asp:ListItem Text="Apple" Value="Apple" />
<asp:ListItem Text="Banan" Value="Banana" />
</asp:DropDownList>
</div>
</form>
</body>
</html>
Demo
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<style type="text/css">
body
{
font-family: Arial;
font-size: 10pt;
}
</style>
<script type="text/javascript">
window.onload = function () {
var select = document.getElementById("ddlFruits");
select.removeChild(select.options[0]);
}
</script>
</head>
<body>
<select name="ddlFruits" id="ddlFruits">
<option value="Mango">Mango</option>
<option value="Apple">Apple</option>
<option value="Banana">Banan</option>
</select>
</body>
</html>
Demo
