Objective:To compare the difference of serum 1,25-dihydroxyvitamin D3(1,25(OH)2D3) between type 2 diabetes mellitus patients and normal persons,and to analyze the relationship between vitamin D3 and type 2 diabetes mellitus. Methods:110 patients with type 2 diabetes mellitus were selected as the case group,and 105 healthy people were selected as the control group. ELISA was used for the detection of serum 1,25-dihydroxyvitamin D3. Questionnaire survey was performed,and clinical and biochemical indexes were also detected. Results:There was a significant difference in serum 1,25(OH)2D3 level between the case and control group (P < 0.01). There was a significant negative correlation between serum 1,25(OH)2D3 level and fasting blood glucose(rs=-0.696,P < 0.01). Conclusion:Serum 1,25(OH)2D3 in the case group was significantly lower than that in the control group. The higher fasting blood glucose,the lower serum 1,25(OH)2D3.