Proceptive behavior, according to Beach (1976), maintains and accelerates sexual interactions toward the end goal. Such distinctive type of proceptive behavior as darting or hopping of female rats is not apparent in mice. Nevertheless, it seems more reasonable that females may take an active part as much as their male partners also in this species. Twenty sexually experienced females in estrus were paired with 20 naive males of the same strain (ICR/JCL) and the pairs were observed for 6 hours. Eleven males of the 20 pairs successfully ejaculated. Females exhibited lordosis more frequently when they actively approached the male partners than when they were approached and mounted by males. This indicated that the rate of mating success was higher in the case of female's approach. Female's approaching behavior thus possibly plays a role as a proceptive behavior in mice.