To study the relationship between body mass index (BMI) and urinary albumin creatinine ratio in patients with type 2 diabetes mellitus. Methods105 patients with type 2 diabetes mellitus were divided into three groups according to BMI:mild group (n＝20), normal group (n＝30), overweight group (n＝30) and obesity group (n＝25). The blood glucose, FBG, 2 hPG, HbA1c, TG, TC, LDL, HDL, SCr, BUN and UACR of the four groups were compared. Pearson linear correlation was used to analyze the correlation between BMI and UACR. Results HbA1c, TG, TC and LDL in normal group were significantly higher than those in mild group, but lower than those in overweight and obesity group; HDL of normal group was significantly lower than that of mild group, but higher than that of overweight and obesity group (P＜0.05). SCr, UACR and BUN in overweight and obesity groups were significantly higher than those in mild and normal groups (P＜0.05). Pearson linear correlation analysis showed that BMI＜18.5 kg/m², BMI 18.5－24.0 kg/m² had no correlation with UACR (P＞0.05), BMI 24.0－28.0 kg/m², BMI≥28 kg/m² had positive correlation with UACR (P＜0.05). ConclusionThere are obvious segmental changes in the correlation between different BMI and UACR in patients with type 2 diabetes mellitus, and clinical diagnosis and treatment should be combined with various examination indexes.