ABSTRACT BACKGROUND: Self-efficacy is one of the most likely determinants of glucose self-management and self-monitoring by diabetic patients. Also, social capital is one of the effective social factors that may affect health behaviors. The aim of this study was to evaluate the relationship between social capital and self-efficacy in women with gestational diabetes mellitus (GDM).METHODS: This descriptive- analytical cross-sectional study was conducted on 212 women with GDM in two diabetes center in Mazandaran, north of Iran, from April to July 2019. Patients' social capital and self-efficacy levels were measured using the Social Capital Questionnaire (SCQ) and Confidence in Diabetes Self-Care Scale questionnaire, respectively.RESULTS: Among eight dimensions of social capital, the highest and the lowest mean scores were related to proactivity (21.3) and tolerance of diversity (5) dimensions. The mean (standard deviation=SD) of self-efficacy total score was 40.7(18.2), indicating moderate self-efficacy. Pearson correlation coefficient indicated that there was significant positive relationship between all dimensions of social capital and self-efficacy (p˂0.05). In addition, the results of multiple regression analysis indicated that community participation, neighborhood connections, family and friends' connections, tolerance of diversity and work connections, explained 55% of the variance in self-efficacy in women with GDM (p˂0.05).CONCLUSION: The results highlighted a significant positive relationship between social capital and self-efficacy in women with GDM. Improving women’s social capital may enhance their self-efficacy in controlling GDM.KEYWORDS: Self-Efficacy; Diabetes, Gestational; Social Capital