<script type="text/javascript">
function ClientValidate(source, arguments) {
if (parseInt(arguments.Value)>10)
arguments.IsValid = true;
else
arguments.IsValid = false;
}
</script>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Button" />
<asp:CustomValidator ID="CustomValidator1" runat="server"
ControlToValidate="TextBox1" ErrorMessage="CustomValidator" ClientValidationFunction="ClientValidate"></asp:CustomValidator>