What version of JQuery are you using and in what browser? FYI - You question appears to really be isolated to JQuery and what has already been rendered to the browser, so you may want to take off the spring related tags.
try making the change like this: $("input[value='Female']").prop('checked',true);
<html>
<head>
<script src="jquery-1.9.1.js"></script>
</head>
<body>
<form>
<input type="radio" path="gender" id="Male" name="sex" value="Male" checked="checked" />Male
<br />
<input type="radio" path="gender" id="Female" name="sex" value="Female" />Female
<div id="test">my test</div>
</form>
<script>
alert("hello");
$("input[value='Female']").prop('checked',true);
alert("bye");
</script>
</body>
</html>