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<title>让ie6也支持max-width，和max-height实现图片等比例缩放</title>
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*{ margin:0; padding:0;}
ul{ list-style:none;}
img{ border:0;}
.box{ width:450px; height:auto; margin:100px; padding:10px;}
.box li{ float:left; width:100px; height:100px; padding:1px; margin:5px; border:1px solid #ccc; text-align:center;}
.box li img{ max-width:100px; max-height:100px;_width: expression(this.width > 100 && this.width > this.height ? 100 :true);
_height: expression(this.height > 100 ? 100 : true);}
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<li><a href="#"><img src="img/01.jpg" width="50" height="50" /></a></li>
<li><a href="#"><img src="img/Windows Logo.jpg" /></a></li>
<li><a href="#"><img src="img/04.jpg" /></a></li>
<li><a href="#"><img src="img/06.jpg" /></a></li>
<li><a href="#"><img src="img/09.jpg" /></a></li>
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(转载)让ie6也支持max-width，和max-height实现图片等比例缩放
原文：http://www.cnblogs.com/jdsm/p/3522089.html