这段代码在firefox上可以，但是IE上不行，楼主去查查html4.0或者dom的spec吧。
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
function test()
{
document.f1.s1.options[3].disabled=true;
}
//-->
</SCRIPT>
</HEAD><BODY onload="test()">
<form name=f1>
<SELECT NAME="s1">
<option value=1>1</option>
<option value=2>2</option>
<option value=3 disabled>3</option>
<option value=4>4</option>
</SELECT>
</form>
</BODY>
</HTML>
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
function test()
{
document.f1.s1.options[3].disabled=true;
}
//-->
</SCRIPT>
</HEAD><BODY onload="test()">
<form name=f1>
<SELECT NAME="s1">
<option value=1>1</option>
<option value=2>2</option>
<option value=3 disabled>3</option>
<option value=4>4</option>
</SELECT>
</form>
</BODY>
</HTML>
<OPTGROUP LABEL="碱性金属">
<OPTION>锂 (Li)</OPTION>
<OPTION>纳 (Na)</OPTION>
<OPTION>钾 (K)</OPTION>
</OPTGROUP>
<OPTGROUP LABEL="卤素">
<OPTION>氟 (F)</OPTION>
<OPTION>氯 (Cl)</OPTION>
<OPTION>溴 (Br)</OPTION>
</OPTGROUP>
</SELECT>
<style>
.xx {
}
.xx OPTGROUP{
font-size: 12px;
font-style: normal;
font-weight: normal;
font-variant: normal;
background-color: #CCCCCC;
}
.xx option {
padding-left:0px;
}
</style>
<SELECT name="carCos" class="xx">
<OPTGROUP label="American"></OPTGROUP>
<OPTION value="General Motors">General Motors</OPTION>
<OPTION value="Ford">Ford Motor Company</OPTION>
<OPTION value="Chrysler">DaimlerChrysler</OPTION>
<OPTGROUP label="Japanese"> </OPTGROUP>
</SELECT>