Background and Purpose: Subjective well-being plays a crucial role in human life given the positive impacts it has on mental and physical health, longevity, and quality of life. Therefore, it is important to evaluate and promote subjective well-being and its relevant factors. This study aimed to assess the role of social capital in subjective well-being among Iranian adolescents. Methods: This cross-sectional, analytical study was performed on high school students (10 th to 12 th grades) residing in Birjand city, center of the Southern Khorasan Province, Iran, in 2015. The main inclusion criteria were being a student of public high schools and living with parents. Using multi-stage cluster sampling, 400 students were selected. A demographic characteristics form, the Social Capital Index, and the Adolescent Subjective Well-Being Scale were employed for data collection. The data were analyzed using descriptive statistics (including mean, frequency, and standard deviation) and inferential statistics (e.g., Pearson and Spearman's coefficients, step-wise multiple regression, Mann-Whitney U test, and Kruskal-Wallis test). Results: The participants reported a high level of social capital (89.06±12.87) and a moderate level of subjective well-being (29.82±6.91). There was a significant positive correlation between social capital and subjective well-being scores (r=0.5, P<0.001). Furthermore, 32% of the variance of subjective well-being was explained by social capital and gender (girls; R 2 =0.32, F=95.24, P <0.001). Conclusion: Improving social capital among social institutions such as family, school, and other youth-related networks can result in enhanced subjective well-being in adolescents.