In a zoom lens system comprising a front lens group having negative refractive power and a rear lens group having positive refractive power and designed in such a manner that the airspace between said front lens group and rear lens group is varied for zooming, a zoom lens system comprising a rear lens group consisting of a positive lens component, a positive meniscus lens component, a positive meniscus cemented doublet, a negative lens component and a positive lens component, and having a large relative aperture and favorably corrected aberrations.