Try this jQuery sample and adapt it to your need:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm15.aspx.cs" Inherits="WebApplicationCS2.WebForm15" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
<script>
$(document).ready(function () {
var $checkboxlist = $("#<%= CheckBoxList1.ClientID %>");
var $uniqueItemCheckbox = $checkboxlist.find(" input:checkbox[value='Unique Item']");
var $otherCheckbox = $checkboxlist.find("input[type=checkbox]").not($uniqueItemCheckbox);
$uniqueItemCheckbox.change(function () {
if ($(this).prop("checked")) {
$otherCheckbox.prop(
"checked", false
);
}
$otherCheckbox.prop(
"disabled", $(this).prop("checked")
);
});
});
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:CheckBoxList ID="CheckBoxList1" runat="server">
<asp:ListItem>Item 1</asp:ListItem>
<asp:ListItem>Unique Item</asp:ListItem>
<asp:ListItem>Item 3</asp:ListItem>
<asp:ListItem>Item 4</asp:ListItem>
</asp:CheckBoxList>
</div>
</form>
</body>
</html>
Learn
jQuery Tutorial[
^]