The purpose of this study was to use structural equation modeling to examine the effects of trait rumination and reflection on stress response and subjective well-being among Japanese university athletes. One hundred and eighty-two Japanese university athletes (114 males, 68 females, mean age = 20.15 years) participated. Trait rumination was positively associated with stress response and negatively associated with subjective well-being. On the other hand, trait reflection showed a negative association with stress response and a positive association with subjective well-being. In order to develop effective interventions for athletes high in rumination and/or low in reflection, future research should examine the mechanism that explains the different effects of rumination and reflection on athlete mental health.