The purpose of this study was to examine the role of recess as a mediating variable between autism spectrum disorder (ASD) traits and psychosocial maladjustment in children. The participants were 5,366 pairs of general elementary and junior high school students (grades 4–9) and their parents. A path analysis revealed that the higher the ASD traits, the more time was spent on non-interpersonal play during recess. The results of estimating the extent to which the mediating variable, recess time, explained the association between ASD traits and psychosocial maladjustment showed that the indirect effect via recess play ranged from 20% to 60% of the total indirect effects (recess time + friendships) and from 20% to 40% of the total effects (direct effects + indirect effects). Although recess play was regarded as one of the subcomponents of friendship, it explained 65% of the indirect effects of prosocial behavior, 46% of depression, and 26% of aggression, suggesting that the role of recess in friendship is exceptionally large. We consider that psychosocial maladjustments are mediated by recess.