Objective: The study aimed to examine the impact of a supportive school environment on children’s prosocial behavior by investigating the sequential mediating effects of children’s self-esteem and happiness. Methods: Results of the study were obtained by analysing data collected from 633 nine-year-old children in the 10th wave of the Panel Study on Korean Children(2017). The data were analyzed by descriptive statistics, correlation analysis and significance of mediated pathways using SPSS 23.0 and PROCESS macro 3.3. Results: First, children’s self-esteem did not have mediational effects with respect to a supportive school environment and children’s prosocial behavior. Second, children’s happiness had mediational effects with respect to a supportive school environment and children’s prosocial behavior. Lastly, a supportive school environment affects children s self-esteem, which affects children s happiness, thereby promoting children s prosocial behavior. Conclusion/Implications: In order to promote children s prosocial behavior, we should put emphasis on developing a supportive school environment, and increasing children s self-esteem and happiness. It is important that teachers treat children and classmates treat each other with a warm attitude so that they can value themselves and feel happiness in their lives.