<script type="text/javascript"> function check_box() { var count=document.myform.checkThis.length; //var count=document.getElementById('checkThis').length; alert(count); var j=0; for(var i=0;i<count;i++) { if (document.myform.checkThis[i].checked) //if (document.myform.checkThis[i].checked) //document.getElementById('checkThis').checked; ++j; } if(j==0) { alert("至少选择一个!!"); return false; } else { return true; } } </script>