Although school climate plays an important role in the development of adolescent prosocial behaviors and problem behaviors, little is known about the mechanisms underlying school climate's impact on such behaviors, particularly in Chinese adolescents. This study used a multi-informant approach to investigate the mediating role of social-emotional learning (SEL) competencies on the association of school climate with prosocial behaviors and problem behaviors (i.e., internalizing and externalizing behaviors) among Chinese adolescents. A total of 699 students (M[subscript age] = 12.89 years, SD = 0.70) in 7th and 8th grades from three middle schools in Chengdu, China completed measures of perceived school climate and SEL competencies. Their guardians also completed ratings on adolescent prosocial and problem behaviors. As predicted, while perceived school climate was positively associated with adolescent prosocial behaviors, it was negatively related to adolescent internalizing and externalizing behaviors. Analyses using PROCESS further showed that SEL competencies mediated the relationship between perceived school climate and adolescent behaviors. The findings underscored the importance of promoting positive school climate as well as SEL competencies to foster positive adolescent development.