<div style="width:300px;"> 
  <div id="Left" style="float:left;">1<br/>3<br/>5<br/></div> 
  <div id="Right" style="float:right;">2</div> 
</div>
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<script type="text/javascript"> 
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    var heightLeft= $("#Left").height(); 
    var heightRight= $("#Right").height(); 
    if (heightLeft > heightRight) 
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      $("#Right").height(heightLeft); 
    } 
    else 
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      $("#Left").height(heightRight); 
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原文:http://www.cnblogs.com/jsingleegg/p/3953574.html