The projection zoom lens system includes a negative first lens group, a positive second lens group, a third lens group, a positive fourth lens group, a fifth lens group, and a positive sixth lens group. The lens system is nearly telecentric on a reduction side. During zooming, the second to fifth lens groups are moved while the first and six lens groups remain stationary. The third lens group includes a positive lens L.sub.P having a convex surface directed to a magnification side, and a negative lens L.sub.N having a concave surface which is directed to the reduction side and has a curvature stronger than a magnification-side surface of the negative lens L.sub.N. The conditional expression of 5.0.ltoreq.|f.sub.G3/R.sub.LN-2| is satisfied. Here, f.sub.G3 denotes a focal length of the third lens group, and R.sub.LN-2 denotes a radius of curvature of the reduction-side surface of the negative lens L.sub.N.