A zoom lens system comprises, successively from the object side, a first negative lens group and a positive second lens group. The first lens group includes a negative meniscus lens and a positive meniscus lens, the negative meniscus lens and the positive meniscus lens each has at least one aspherical surface. The second lens group includes a first positive auxiliary group and a positive second auxiliary group. The refractive power of the first group is 1/f.sub.1, the refractive power of the second group is 1/f.sub.2, the focal length of the whole lens system f.sub.w when the distance between the lens groups is increased, f.sub.T is the focal length of the whole lens system when the distance between the lens groups is decreased, and they satisfy the following conditional expressions of: 0.9.ltoreq.|f.sub.1|/(f.sub.wf.sub.T).sup.1/2.ltoreq.1.1 and 1.15.ltoreq.|f.sub.1|/f.sub.2.ltoreq.1.35.