<p>This study examined the relationship between leisure activities and life satisfaction among Korean adolescents. Longitudinal data from 2,325 middle school students across three waves (2018–2020) of the Korean Children and Youth Panel Survey 2018 were analyzed using an autoregressive cross-lagged model. The results can be summarized as follows. First, among leisure activities in the first year of middle school, reading negatively influenced life satisfaction in the second year, whereas exercise and physical activity had a positive effect. Second, leisure activities in the second year did not significantly affect life satisfaction in the third year. Third, life satisfaction in the first year was associated with reduced time spent using smartphones for leisure in the second year, and this pattern persisted into the following year. Fourth, exercise and physical activity in the first year positively influenced life satisfaction in the second year, and second-year life satisfaction, in turn, affected participation in exercise and physical activity in the third year. These findings indicate a bidirectional relationship between physical activity and life satisfaction over time. In conclusion, this study provides longitudinal evidence of the relationship between different types of leisure activities and life satisfaction among adolescents from the first to the third year of middle school, highlighting its significance.</p>