See this : http://jsfiddle.net/qzjaQ/1/
$(function() {
 $("#tabs-left").tabs({
     show: {
         opacity:'toggle',
         duration:'normal'
     }
 });
 // getter
 var show = $(".selector").tabs("option", "show");
 // setter
 $(".selector").tabs("option", "show", {
     opacity:'toggle',
     duration: 'normal'
 });
});
See here for explanations..
solved JQuery tabs opacity transition [closed]