Virgin male mice tend to attack pups, but they show behavioral change toward parental behaviors after mating experience. However, the mechanisms of this behavioral change are not well understood. Inhibition of D₂ receptor causes increased blood prolactin (PRL) levels and lowered sexual activities. PRL is important for parental behaviors in female and has effects to activate the medial preoptic area (MPOA) neurons which regulate behavioral choice, attacking or parenting. Therefore, we hypothesized that administration of a D₂ receptor blocker would produce changes toward parental behaviors in virgin male mice. We intraperitoneally administered sulpiride, a D₂ receptor blocker, to virgin male mice 30 min before testing. This procedure was continued for 4 days. However, there was no significant difference in the behavioral pattern toward pups compared with the vehicle group. Next, we administered sulpiride to virgin male mice for 2 weeks which is approximately the same period that male mice show the significant behavioral change toward pups after mating. Long-term administration of sulpiride significantly changed the behavioral pattern from attack to non-attack or parenting. Increased blood prolactin levels following inhibition of D₂ receptors might influence social behavioral choice toward pups in male.