var availableTags = [
  "ActionScript",
  "AppleScript",
  "Asp",
  "BASIC",
  "C",
  "C++",
  "Clojure",
  "COBOL",
  "ColdFusion",
  "Erlang",
  "Fortran",
  "Groovy",
  "Haskell",
  "Java",
  "JavaScript",
  "Lisp",
  "Perl",
  "PHP",
  "Python",
  "Ruby",
  "Scala",
  "Scheme"
];
$( "#tags" ).autocomplete({
  source: availableTags
}).data("ui-autocomplete")._renderItem = function (ul, item) {

    ul.addClass('customClass'); //Ul custom class here

    return $("<li></li>")
    .addClass("liCustomClass") //item based custom class to li here
    .append("<a href='#'>" + item.label + "</a>")
    .data("ui-autocomplete-item", item)
    .appendTo(ul);
}; 

});