To investigate the inhibitory effects of Peonia japonica water extract(PJWE) on skin wrinkle formation, skin wrinkles were induced by both the irradiation of UVB and the application of squalene monohydroperoxide to the backs of hairless mice for 4 weeks. And at the same time experimental materials were applied topically. Wrinkles for the control (C) group were formed as a pattern of deep furrows and thick crests. Whereas wrinkles for the positive control (PC, 0.01% retinoic acid) and experimental(E, PJWE) groups were formed as a pattern of shallow furrows and thin crests, which were similar to that of the normal(N) group. Collagen and elastic fibers in dermis of the PC and E groups were almost intact with a regular arrangement, which were similar to those of the N group. The activity of xanthine oxidase, the free radical generating enzyme, was significantly lower in the E group than the C and PC groups. The activities of superoxide dismutase and catalase, the free radical scavenging enzymes, were much higher in the E group than the C and PC groups and similar to the N group. As for the amount of matrix metalloproteinase-3(MMP-3) expression, PC and E groups were significantly lower than the C group. Therefore, PJWE could be very effective natural herbal material for the inhibition or improvement of wrinkle formation in hairless mice skin.