<script>
function check(){
var flag = false;
if(form1.info_type != null){
    var msglen=form1.info_type.length;
    for(i=0;i<msglen;i++){
      if(form1.info_type[i].checked==true){
        flag = true;
      }
    }
}
if (flag == false)
{
    alert("对不起，请选择")
    return false;
}
}
</script>


<form id="form1" name="form1" method="post" action="" onsubmit="return check();">
<td height=30>A
   <input type="radio" name="info_type" value="A">
   B
   <input type="radio" name="info_type" value="B">
   C
   <input type="radio" name="info_type" value="C">
   <label>
   <input type="submit" name="Submit" value="提交" />
   </label></td>
</form>

?

大家自己看下把 很好理解的 希望对大家有用