$(document).ready(function()
{
$(".main1").change(function()
{
var id1=$(this).val();
var dataString = 'id1='+ id1;

$.ajax
({
type: "POST",
url: "sub_cat1.php",
data: dataString,
cache: false,
success: function(html)
{
$(".id1").html(html);
} 
});

});
});