Call setThumbValueAt() method of HSlider to change the slider value
<?xml version="1.0"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:Script> public function adjustThumb(s:HSlider):void { s.setThumbValueAt(0,4); } </mx:Script> <mx:HSlider id="slider1" /> <mx:Button id="myButton" label="Set Thumb" click="adjustThumb(slider1);" /> </mx:Application>