ObjectiveTo study the relationship between serum 25-hydroxy vitamin D3[25-(OH) D3] level and diabetic nephropathy(DN). Methods Three hundred and one patients with diabetic mellitus were enrolled in the study, including 97 cases with diabetic nephropathy(DN group) and 204 cases without diabetic nephropathy(non-DN group). Sex, age, diabetes duration, height, weight, waist circumference(WC), hip circumference(HC) were recorded, and body mass index(BMI), waist/hip ratio(WHR) were calculated. Serum 25-(OH)D3 levels were measured by enzyme-linked immunosorbent assay(ELISA). The correlation of 25-(OH)D3 level with BMI, WC, HC, WHR, diabetes duration was analyzed. Results There were not statistical significances in sex, age, height, weight, WC, HC , BMI and WHR between DN and non-DN groups(P>0.05). However, the diabetes duration in DN group was longer than that in non-DN group and serum 25-(OH)D3 level in DN group was lower than that in non-DN group. Serum 25-(OH)D3 level was negatively correlated with the diabetes duration(r=-0.174,P<0.05), and not correlated with BMI, WC, HC and WHR(r=0.041,0.111,0.071 and 0.001,P>0.05). Conclusion DN patients have longer diabetes duration and lower serum 25-(OH)D3 level than non-DN patients.