$(document).ready(function() { var randomImages = ['header-bg-atdusk','header-bg-2010buckle','header-bg-fadingsun','header-bg-ra2010champ','header-bg-reinerboot']; var rndNum = Math.floor(Math.random() * randomImages.length); $("div#header").css({ background: "white url(assets/images/layout/default/" + randomImages[rndNum] + ".jpg) center center no-repeat" }); });