Abstract: A projection zoom lens system of the present invention for projecting image onto a screen from a light modulator such as a DMD includes a first lens group having a negative refractive power and a second lens group having a positive refractive power arranged in this order from the screen side. An outer diameter LD of the last lens and a back focus at the wide-angle end Bfw of the projection zoom lens system satisfy the condition below.0.3<LD/Bfw<0.5 (A).Further, at least one of surfaces of the last lens is aspheric. Therefore, even though the back focus is long and a diameter of the last lens is small, it is possible to provide a compact projector lens system having excellent optical performance with the only nine lenses arrangement.