Collective nostalgia refers to the nostalgic feelings of individuals towards the events experiencedby group members or collective historical events, and is a core variable that facilitates group identity.Using a recall writing paradigm, the subjects were randomly divided into a collective nostalgia group, anindividual nostalgia group, and a control group. The results showed that: (1) initiating collective nostalgiacan promote positive in-group behavior. (2) Compared with the individual nostalgia group and thecontrol group, collective self-esteem mediated the relationship between collective nostalgia and positiveingroup behavior. The results revealed that collective nostalgia promotes positive ingroup behavior and itsmechanism, which enriches intergroup emotion theory and group participation theory.