Background Microalbuminuria (MAU) and ambulatory arterial stiffness index (AASI) may predict cardiovascular events and death. However,there is little information about the correlation between the two parameters in patients with type 2 diabetes mellitus (T2DM) . Therefore,we examined the association of MAU with 24-hour AASI in patients with T2 DM. Methods A total of 189 patients with 24-hour ambulatory blood pressure monitoring (24h-ABPM) who were hospitalized from January 2011 to January 2017 were selected. 136 patients without hypertension were screened. The subjects were divided into two groups according to urinary albumin-to-creatinine ratio (u ACR) . MAU group was defined as u ACR of 30-299 mg/g (n=69),NMAU group was defined as u ACR <30 mg/g (n=67) . AASI was calculated as 1 minus the regression slope of diastolic blood pressure (DBP) value vs. systolic blood pressure (SBP) value according to ABPM. The differences of clinical and biochemical indicators between the two groups were determined. The correlation between AASI and MAU was analyzed by unconditional forward stepwise logistic regression. Results Patients with MAU had significantly higher level of diabetic duration,TC,LDL-C,Scr,AASI and lower e GFR than NMAU group (P<0.05) . Using MAU as the dependent variable (1 with MAU and 0 without MAU),LDL-C,decreased e GFR,AASI were independent risk factors of MAU in patients with T2 DM. The ROC curve of AASI in predicting the risk of MAU showed when AASI was 0.48,the area under the curve was the largest 0.659 (95 % CI 0.568-0.750,P=0.001) .The sensitivity was 71.0% and the specificity was 56.7%. Conclusions Patients with MAU have higher AASI than patients without MAU. As a new index of arterial stiffness,AASI is associated with MAU,and could independently predict MAU in patients with T2DM. Background, Microalbuminuria (MAU) and ambulatory arterial stiffness index (AASI) may predict cardiovascular events and death. However, there is little information about the correlation between the two parameters in patients with type 2 diabetes mellitus (T2DM). Therefore, we examined the association of MAU with 24-hour AASI in patients with T2 DM. Methods A total of 189 patients with 24-hour ambulatory blood pressure monitoring (24h-ABPM) who were hospitalized from January 2011 to January 2017 were selected. 136 patients without hypertension were screened MAU group was defined as u ACR of 30-299 mg / g (n = 69), NMAU group was defined as u ACR < 30 mg / g (n = 67). AASI was calculated as 1 minus the regression slope of diastolic blood pressure (DBP) value vs. systolic blood pressure (SBP) value according to ABPM. The differences of clinical and biochemical indicators between the two groups were Results The patients with MAU had significantly higher level of diabetic duration, TC, LDL-C, Scr, AASI and lower eGFR than NMAU group (P <0.05) . Using MAU as the dependent variable (1 with MAU and 0 without MAU), LDL-C, decreased e GFR, AASI were independent risk factors of MAU in patients with T2 DM. The ROC curve of AASI in predicting the risk of MAU showed when AASI was 0.48, the area under the curve was the largest 0.659 (95% CI 0.568-0.750, P = 0.001). The sensitivity was 71.0% and the specificity was 56.7%. Conclusions Patients with MAU have higher AASI than patients without MAU As a new index of arterial stiffness, AASI is associated with MAU, and could independently predict MAU in patients with T2DM.