The resizable feature is not supported in panel plugin. But you can wrap a resizable <div> around the panel. Set 'fit' property of panel to true and call 'resize' method when the wrap <div> is resizing.
<div id="ccc" style="width:400px;height:300px;padding:5px">
<div id="0" class="easyui-panel" data-options="fit:true,closable:true,collapsible:true,maximizable:true"/>
</div>
$(function(){
$('#ccc').resizable({
edge:5,
onResize:function(){
$('#p').panel('resize');
},
onStopResize:function(){
$('#p').panel('resize');
}
});
});