The study-leisure balance of adolescents is very important especially in Korea for children and adolescents’ health and growth because Korean adolescents have been suffered from a heavy workload and long study time. However, there is a dearth of research focusing on adolescents’ study-leisure balance, leisure time, leisure expense, and happiness unlike researcher’s interests on adults’ work-leisure balance and many leisure behaviors including leisure time and expense. Thus, the purpose of the study is to explore the relationships among adolescents’ study-leisure balance, their felt sufficiency of leisure time and leisure expense and happiness. The total 980 middle school student data were selected from ‘2019 Children & Adolescents Culture & Leisure Research’and used for the analysis. After frequency analyses, descriptive statistics, and correlation-analyses were run, One-way ANOVA with a post-hoc and Multiple Regression Analysis on the variables were performed. The results showed that the felt sufficiency of leisure time and leisure expense were the highest in the leisure-focused group, the second highest in the study-leisure balanced group, and the lowest in the study-focused group. However, the happiness level was higher in the study-leisure balanced group and the leisure-focused group than the study-focused group. According to the results of the regression analysis, only the felt sufficiency of leisure time, not leisure expense, influenced the happiness level of adolescents.