The effect of chromium doping on the defect-induced ferromagnetism of Zn1-xCrxO films was investigated in this study. X-ray diffraction and x-ray photoelectron results confirm Cr substitution at Zn sites in the ZnO host lattice. A parabolic dependence of the saturation magnetization on the stoichiometric variable x was observed. Photoluminescence and magnetic results indicate that magnetic moments in Zn1-xCrxO films stem from Zn vacancies on the film surface or at grain boundaries. As the variation in saturation magnetization is consistent with that in surface morphology, the ferromagnetism in Zn1-xCrxO films is sensitive to the morphological modification caused by Cr doping.