This study aims to examine the mediating effects of peer relationship and self-esteem on the relationship between psychosocial school environment and subjective happiness. Data from the 13th year of the Korea Welfare Panel Study, which covered data from 319 adolescent students, were used for analysis. The results revealed that, first, psychosocial school environment, peer relationship, and self-esteem were positively and significantly correlated with subjective happiness. Second, psychosocial school environment, peer relationship, and self-esteem exerted a positive effect on subjective happiness. Finally, peer relationship and self-esteem played mediating roles in the relationship between school environment and subjective happiness.