Online hate is widely identified as a social problem, but its social psychological dimensions are yet to be explored. We used an integrative social psychological framework for analyzing online hate offending and found that both personal risk factors and online group behavior were associated with online hate offending. Study 1, based on socio-demographically balanced survey data (N = 1200) collected from Finnish adolescents and young adults, found that impulsivity and internalizing symptoms were positively associated with online hate offending. Furthermore, social homophily was positively associated with online hate offending but only among those with average or high level of internalizing symptoms. Social identification with online communities was not associated with hate offending. In Study 2, based on a vignette experiment (N = 160), online hate offenders were more likely than others to rely on in-group stereotypes (i.e. self-stereotype) in anonymous online interaction and, as a consequence, follow perceived group norms. These associations were found only when a shared group identity was primed. We conclude that both personal risk factors and group behavior are related to online hate but they have different implications for reducing hateful communication in social media.