The main objective of this study is to investigate the impact of organizational citizenship behavior on job performance with the mediating role of social capital. Given the nature of this research, which seeks to examine the relationship between the research variables, the study is classified as a survey. The statistical population consists of all employees of private hospitals in Sari, Iran, totaling 185 individuals, as confirmed by the Mazandaran Province Health Network, who were employed in 2021. The sample size was determined to be 120 individuals based on the Krejcie and Morgan table, selected through stratified random sampling (46 men and 74 women). Data collection tools included standard questionnaires by Podsakoff et al. (1990) for organizational citizenship behavior, Nahapiet and Ghoshal (1998) for social capital, and Patterson (1992) for job performance. Data analysis was conducted using PLS2 software. The results revealed that organizational citizenship behavior influences job performance, organizational citizenship behavior affects social capital, and social capital impacts job performance. However, social capital does not play a mediating role in the relationship between organizational citizenship behavior and job performance among employees.