This paper presents a survey on relationship between social capital and knowledge management for knowledge based organizations. This research is of descriptive-correlation one and the sample includes 100 faculty members of non-governmental institutes of Babol city. The instrument was questionnaire and the analysis performed using SPSS17 and Lisrel 8.8 software. Pearson correlation test, multiple regression analysis route analysis, and structural equations modeling were used as statistical tests. The research showed that social capital had direct and significant effect on knowledge management in 99% confidence interval. Among the dimensions of social capital, trust and social norms with knowledge application; trust with knowledge acquisition; trust and social norms with knowledge transfer; trust and networks association with knowledge creation; and trust, social norms and networks association with knowledge record had significant and positive effects in 95% confidence interval. Social capital was effective on knowledge management and knowledge based organizations could promote knowledge creation, acquisition, record, application and transfer process by improving social capitals.