Objectives: The purpose of this study was to investigate the effect of youth activities (participation and satisfaction) on happiness, focused on the mediating effect of academic engagement. Methods: The empirical analysis data of this study was extracted from the 3rd wave data of the Korean Children and Youth Panel Survey (KCYPS, 2018). The subjects of this study were 9th grade 2,384 adolescents. The data were analyzed with Pearson’s correlation coefficient, regression analysis, and the Sobel test. Results: The significant factors related to academic engagement were youth participation (B=-0.22, p<0.05) and satisfaction (B=0.34, p<0.001). A higher level of satisfaction with youth activities was associated with a higher level of happiness (B=0.04, p<0.001). Academic engagement was a partial mediator between the satisfaction of youth activities and happiness. Conclusions: The findings of this study suggest that further research is needed on practical methods and educational programs that can increase satisfaction with youth activities, and improve academic engagement in order to promote happiness in adolescents.