Objective To investigated the correlation of between 25-hydroxyvitamin D3 levels and blood lipids, insulin function in diabetic mellitus patients. Methods Seventy eight patients with type 2 diabetes, seventy eight patients with type 1 diabetes and seventy eight health examiner were recruited in the present study. According to the level of 25-hydroxyvitamin D3, they were divided into VD3<50 nmol/L group (n = 69) and VD3 ≥ 50 nmol/L group (n = 165), and the blood lipid index and insulin function were compared between the two groups. Results ① The statistical differences in age, BMI, glycosylated hemoglobin, fasting blood glucose, 2-hour blood glucose, fasting c-peptide, 2-hour serum c-peptide, 25-hydroxyvitamin D3 and insulin function between the diabetic T1DM group, diabetic T2DM group and control group were significant (P < 0.05); ② Serum cholesterol was decreased and insulin function was increased in the VD3<50 nmol/L group compared to VD3≥50 nmol/L group (P < 0.05).③There were negative correlations between Vitamin D3 and BMI with islet β-cell index in type 1 diabetic patients (r = -0.259, P < 0.05; r = -0.491, P < 0.05); there was negative correlation between Vitamin D3 level and total cholesterol level (r = -0.227, P < 0.05) in type 2 diabetic patients. Conclusions 25-hydroxyvitamin D3 level is closely related to TC and insulin beta cell function in diabetic patients.