Edit in JSFiddle

$(document).ready(function() {     
    var move = "expand";
    $('div').click(function(){
            if (move == "expand"){
                $('div').animate({width:"30px",height:"30px"},500);
                move = "shrink";
            } else {
                $('div').animate({width:"80px",height:"80px"},500); 
                move = "expand";
            }
    });		
});

<div></div>

div{
    background:#333;
    width:80px;
    height:80px;    
}