One of the significant capabilities of any organization that can contribute to performance improvement and productivity is social capital. The current study, therefore, aims to investigate the effects of social capital on performance improvement in manufacturing industries. In this study the model of Nahapit and Goshal was applied to measure the social capital. To collect data Anidro Krishna standard questionnaire, which is published by the World Bank, was employed, and revised to adapt to cultural and organizational structure of Iran institutions. In addition its validity was confirmed by some experts.The output was confirmed by Cranach's coefficient alpha. To measure social capital, 1100 questionnaires were distributed among 1668 workers in 11 factories producing Detergent, Hygienic and Cosmetic products, from which 647 were collected.To investigate performance, 7 financial and non-financial indexes were selected and then homogenized. The research method was descriptive and analytical. In addition, interviewees were middle-level managers, office workers and factory workers.Spearman correlation coefficient was employed to conduct statistical analysis of the data as the design of the study was correlational. The results show that in these eleven companies, there is a significant relationship between social capital and some indexes of their performance. In other words, some indicators of performance are improved through increasing social capital.