Objectives: The aim of this research was to study the predictive role of self-efficacy, belief of treatment effectiveness, social support and doctor-patient relationship on diabetes Mellitus self-management. Method: 500 type II diabetes outpatients (245 men and 255 women) presenting to Shariati Hospital in Tehran were selected by convenience sampling. The subjects completed the scales related to diabetic self-care, self-efficacy, belief of treatment effectiveness, social support and doctor-patient relationship. Data were analyzed using Pearson correlation coefficient and multiple regression analysis. Results: There was a significant and positive relationship between self-efficacy, belief of treatment effectiveness, doctor-patient relationship, social support and diabetes self-management (p<0.001). Self-efficacy, belief of treatment effectiveness and social support were capable of predicting diabetes self-management variance significantly (F=1.326, df=3 and 310, p<0.001) and explain 89% of diabetes self-management. Conclusion: Belief of treatment effectiveness, social support and especially, self-efficacy, are important self-management activities in diabetes Mellitus. Therefore, provision of improvement and enrichment programs for self-efficacy, are helpful for the improvement of self-care behaviors and the reduction of diabetes Mellitus associated harm.