Purpose This study focuses on two aspects of academic performance, namely achievement in courses and research performance. Design/methodology/approach The statistical population of the study consisted of all postgraduate English as a Foreign Language (EFL) students at Iranian national universities in the academic year 2022–2023. The research method used in this study was the survey method, and the data were collected through a questionnaire. The research sample included 360 Iranian postgraduate EFL students who were selected by proportional stratified sampling. Findings The results indicated that social capital had a significant, positive effect on the academic performance of postgraduate students. The dimensions of social trust, a subcategory of social capital, had a significant impact on academic performance in general and on course-related achievement and research performance in particular. Intimacy of network, size of social network, quality of network and access to network significantly affected academic performance from most to least, respectively. Social implications The results suggest strengthening intimate relationships and trust in the university environment, fostering continuous interactions between professors and students in informal networks and enhancing social trust for higher achievements at university.
