ffx,
Используй событие
change.
<!DOCTYPE html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<script src="http://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
<select multiple="multiple" size="5">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
</select>
<select multiple="multiple" size="5">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
</select>
<script type="text/javascript">
$(document).on('change', 'select[multiple]', function (e) {
alert($(this).val())
e.preventDefault();
});
</script>
</body>
</html>