Ostracism and school engagement have important implications for adolescents' academic perseverance and success. However, limited previous studies have investigated the mediating effects of school engagement on the association between ostracism and academic achievement in the Chinese cultural context. The present study fills in this research gap by examining the mediating effects of emotional engagement, cognitive engagement, and behavioral engagement on the association between ostracism and adolescents' academic achievement. Clustered random sampling was employed, and a total of 728 adolescents (52.6% female) were recruited as participants. The results showed that ostracism was negatively associated with academic achievement. Ostracism was negatively associated with emotional engagement and cognitive engagement, which in turn were related to worse academic achievement. Notably, within the Chinese cultural context, behavioral engagement did not exhibit a mediating effect between ostracism and academic achievement. The findings of the present research have theoretical and practical implications for curtailing ostracism and improving adolescents' academic achievement.