The purpose of this study was to investigate the effect of school climate on students' social well-being with the mediating role of social capital. The research method was descriptive-correlational based on structural equation modeling. The statistical population of the study was comprised of all vocational high school students in Hirmand city (Sistan and Baluchestan Province) in 2021-2022 academic year (N= 622). A number of 238 students were selected through random stratified sampling method (by gender) and were given the Social Capital Questionnaire for ‎ Adolescent Students (Paiva et al., 2014), School Climate Measure–Student (Lee et al., 2017) and Well-being Social Inventory (Keyes, 1998).The  Kolmogorov-Smirnov test, Pearson correlation coefficient and structural equation modeling were used to analyze the data using SPSS and SmartPLS software. Correlation coefficient results showed a positive, significant relationship between school climate, social well-being and students’ social capital. The results of structural equation modeling demonstrated that the direct effect of school climate on students' social well-being was positive and significant. Moreover, the indirect impact of school climate on students' social well-being through the mediation of social capital was positive and significant. Hence, it can be concluded that improving the school climate not only directly boosts students’ social well-being but also enhances their social well-being by increasing students’ social capital.