Background: Type 2 diabetes mellitus (T2DM) and Vitamin D deficiency, are too common disorders in the world. Various investigations argues the association between two diseases, however, findings are contradictory and controversial. The aim of the present study was to examine the effect of complementary vitamin D supplementation on improvement of various glycemic parameters in T2DM.Methods: In a double blind randomized clinical trial, 60 persons of T2DM patients were selected and divided into 2 groups with 30 patients. Group 1 were treated with oral Vitamin D (50, 000 unit /week for 12 week), and group 2 were treated with placebo drug.Findings: The age of studied population were between 34 to 76 years and the mean age was 55 ± 10.7 years. Age, sex, BMI and serum levels of HbA1c and 25 (OH) vitamin D were not significantly different between two groups before the study. After 12 weeks treatment intervention, no significant difference was found in serum HbA1c and lipids between two groups.Conclusion: In this study weekly vitamin D supplementation for 12 weeks had not significant decremental effect on HbA1c and lipid profiles, however, further studies needs to evaluate clinical usefulness of our findings.