The present invention relates to a zoom lens assembly employing a four lens group design, which in sequence from an object end thereof to an image end thereof has a first lens group having a positive focal length; a second lens group having a negative focal length; a third lens group having a positive focal length; and a fourth lens group having a positive focal length. In the course of zooming, the third lens group moves serving as a light collector and an assisting compensator for the fourth lens group, so that the diameter of the elements behind the diaphragm can be decreased, which in turn decreases the total length and diameter of the overall zoom lens assembly, meeting the demands of miniaturization of zoom lens assembly without compromising image quality into consideration.