Serotonin (5-HT) is the neurotransmitter which has been strongly implicated in aggression in species ranging from invertebrates to humans. However, little is known about how the 5-HT system is modulated when animals engage in species-typical (adaptive) or escalated aggressive behavior. Previously, we have shown that glutamatergic input in the dorsal raphe nucleus (DRN) is increased when male mice are engaging in an elevated level of aggressive behavior after social provocation. We found that glutamatergic projections from the lateral habenula (LHb) to the DRN were activated by the social provocation, and optogenetic activation of the LHb-DRN projecting neurons increased aggressive behavior of male mice. Anatomical analysis showed that DRN neurons that receive input from the LHb were mainly non-serotonergic and they project to the ventral tegmental area (VTA). Indeed, optogenetic activation of the DRN to VTA projecting neurons increased inter-male aggression. On the other hand, we found that optogenetic activation of 5-HT neurons blocked social instigation-heightened aggression without affecting species-typical level of aggression. These results indicate that the DRN contains both aggression-accelerating neurons and aggression-decelerate neurons in the situation of social provocation.