BACKGROUND: Recent reports suggest that the intake of vitamin D and calcium may influence insulin resistance. The aim of this study was to assess the effects of vitamin D and calcium intervention on the improvement of blood glucose and insulin resistance in patients with type 2 diabetes mellitus (DM). METHODS: Fasting blood glucose, glycosylated hemoglobin A1c (HbA1C), serum 25(OH)D3, serum lipid levels, insulin secretion, and activity and dietary surveys were analyzed in type 2 DM patients both before and after a 12-week vitamin D and calcium intake intervention. RESULTS: The serum 25(OH)D3 level was found to be negatively correlated with insulin resistance and fasting blood glucose. Calcium intake level was also negatively correlated with insulin resistance. Fasting blood glucose, HbA1C, and HOMA-IR decreased significantly (P <0.05) following vitamin D and calcium intake intervention in the medical nutrition therapy (MNT) group, while there was no such change observed in the control group. Dietary calcium and vitamin D intakes were significantly (P <0.05) higher in the MNT group than in the control group. The concentrations of serum 25(OH)D3 and insulin secretion increased slightly in the MNT group following the 12-week intervention; however, these results did not reach statistical significance. CONCLUSION: The results of the present study indicate that calcium and vitamin D intervention may be helpful in improving fasting blood glucose, HbA1C, serum 25(OH)D3 and HOMA-IR in patients with type 2 DM who have insufficient serum 25(OH)D3 concentrations.