Introduction: The aim of the present study was to evaluate the effect of vitamin D on glycemic control and biochemical indices in type 2 diabetes. Methods: This randomized double blind placebo-controlled clinical trial was conducted on 80 patients with type 2 diabetes mellitus (T2DM) referred to Shahid Beheshti hospital. These patients were randomly classified into case and control groups. Case group consumed 50,000 IU of vitamin D once a week for 12 weeks and control group placebo. Biochemical and lipid parameters and vitamin D3 were measured in two groups. Glycosylated hemoglobin (HbA1c) was assessed by latex enhance immunoturbidimetric assay. Results: There was no significant difference between case and control groups in terms of age, sex, body mass index and used medications. The mean vitamin D level in case and control groups before intervention was 15.06 ±3.307 and 15.83± 2.509 ng/ml and after intervention was 49.77 ±15.73 and 14.91±3.13 ng/ml respectively. The mean fast blood sugar in case and control groups after intervention was 156.565±32.23 and 147.75±35.06 mg/dl, respectively. The mean HbA1c in case and control groups before intervention was 7.59± 0.39 % and 7.66± 0.38 % and after intervention was 7.26 ± 0.60 and 7.60 ± 0.38, respectively. Moreover, significant difference was seen between case (20.2± 5.74 IU/L) and control groups (23.35± 7.80 IU/L) in terms of alanine aminotransferase, after intervention. Conclusion: According to these findings, vitamin D supplementation possibly through decreasing HbA1C and hepatic alanine aminotransferase could improve diabetes complications.