The current research consisted of three studies (overall N = 338; 59 men; mean age = 19.98; SD = 1.75), which aimed to examine whether ostracism promotes aggression through enhanced feelings of rule negligence by adopting a multi‐method approach. Participants were undergraduate students in a public university in Hong Kong and they only participated in one of the three studies. The results showed that ostracized participants reported higher levels of rule negligence and aggression than non‐ostracized participants (Studies 1 and 2). Moreover, enhanced feelings of rule negligence significantly mediated the relation between ostracism and aggression (Studies 1 and 2). In addition, priming ostracized people with the importance of following social rules weakened the effect of ostracism on aggression (Study 3). In sum, these findings highlight the critical influence of rule negligence in understanding when and why ostracism promotes aggression and how to diminish such an effect. Implications were discussed.