Try this,
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<asp:checkbox id="chkTest" runat="server" xmlns:asp="#unknown" /> Toggle Enable/Disable
<br />
text1 <asp:textbox id="TextBox1" runat="server"></asp:textbox> <br /><br />
text2 <asp:textbox id="TextBox2" runat="server"></asp:textbox> <br /><br />
text3 <asp:textbox id="TextBox3" runat="server"></asp:textbox> <br /><br />
text4 <asp:textbox id="TextBox4" runat="server"></asp:textbox>
<script language="javascript" type="text/javascript">
$(function () {
$('#<%= chkTest.ClientID %>').click(function (e) {
var textBox1 = $('#<%= TextBox1.ClientID %>');
var textBox2 = $('#<%= TextBox2.ClientID %>');
if (this.checked) {
textBox1.attr('disabled', true);
textBox2.attr('disabled', true);
}
else {
textBox1.removeAttr('disabled');
textBox2.removeAttr('disabled');
}
});
});
</script>