Hi Meenakhi,
Please try the following approach.
<head runat="server">
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script type="text/javascript">
$("[id*=Submit]").live("click", function () {
var flag = true;
$(".ddl").each(function () {
if ($(this)[0].selectedIndex <= 0) {
flag = false;
}
});
if (!flag) {
alert("Any of the ddl can not be unselected.");
}
return flag;
});
</script>
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="DropDownList1" runat="server" CssClass="ddl">
<asp:ListItem Text="Please Select" Value="0" Selected="True"></asp:ListItem>
<asp:ListItem Text="Asp Forums" Value="1"></asp:ListItem>
<asp:ListItem Text="Asp Snippets" Value="2"></asp:ListItem>
<asp:ListItem Text="jQueryFAQS" Value="3"></asp:ListItem>
</asp:DropDownList>
<asp:DropDownList ID="DropDownList2" runat="server" CssClass="ddl">
<asp:ListItem Text="Please Select" Value="0" Selected="True"></asp:ListItem>
<asp:ListItem Text="Apple" Value="1"></asp:ListItem>
<asp:ListItem Text="Mango" Value="2"></asp:ListItem>
<asp:ListItem Text="Banana" Value="3"></asp:ListItem>
</asp:DropDownList>
<asp:Button ID="Submit" Text="Ok" runat="server" />
<br />
</div>
</form>
</body>