Aggression is associated with numerous psychiatric disorders. Evidence suggests that lithium decreases aggression in humans and rats. The effects of lithium on aggression related behavior, and in particular shock-induced aggression, has not been as thoroughly explored in mice. Male mice were treated with lithium and tested in the shock-induced aggression and dominance tube tests. Mice treated with lithium were also assessed for thermal pain and shock sensitivity in the hot plate and jump-flinch tests. In the shock-induced aggression paradigm chronic lithium significantly decreased both the frequency and duration of attacks, without affecting social interaction or behavior in the dominance tube. Acute lithium significantly decreased the total duration of attacks and social interaction but did not affect behavior in the dominance tube test. Neither treatment regimen had an effect on temperature sensitivity in the hot plate test or on activity levels in the open field. However, chronic lithium modified the response of mice to shock in the jump-flinch test, but not at the shock level used in the aggression test. The results of this study indicate that lithium decreases shock-induced aggression in mice, but effects on baseline response to shock confound interpretation of this behavioral effect of lithium.