Little is known about the genetics of social approach-avoidance behaviors. We measured social approach-avoidance of prepubescent female C57BL/6J, DBA/2J, FVB/NJ, AKR/J, A/J, and BALB/cJ mice towards prepubescent DBA/2J female mice. C57BL/6J mice showed the greatest predominance of approach, while BALB/cJ mice showed the greatest predominance of avoidance. Thus, this phenotype is affected by spontaneous genetic variation in mice and can be measured in an assay useful for future neurogenetic studies.