Aggressive behavior is an important prerequisite for acquiring and maintaining feeding resources, territory and mating partners and, therefore, for the survival of an individual and the species. However, dysregulation of aggression among conspecifics can lead to severe injury and death. Aggression is prominently seen when a disturbance occurs in the fine balance of neurotransmitters such as 5-hydroxytryptamine, gammaaminobutyric acid, dopamine, and receptor subtypes. The current study evaluated the in-vivo anti-aggressive potential of a standardized extract of Alstonia scholaris leaves. The extract of Alstonia scholaris was evaluated for its potential effects against defensive and offensive aggressive behavior models of rodents by oral administration at 250, 500 mg/kg BW dose levels once daily for 14 consecutive days as a suspension in a carboxymethylcellulose CMC, diazepam 1 mg/kg, p.o. was used as a standard anti-aggressive agent. Control group animals were given an equal volume of vehicle 10%, v/v, CMC suspension. The anti-aggressive activity was evaluated using the following validated models of aggression, viz.: Isolation-Induced Aggression, Resident-Intruder Aggression, and Water Competition Test, in Swiss albino mice. As a result, methanolic extract of Alstonia scholaris MAS showed dose dependant anti-aggressive activity in the aforementioned, validated models of aggression. This suggests that the MAS has a promising anti-aggressive activity qualitatively comparable to that of diazepam.