Measurement of serum glycated albumin (GA) is accepted as an alternative method to evaluate chronic glycemic control in diabetic patients in whom measurement of HbA_1c is inadequate for some reason. Although GA levels are known to be influenced by serum albumin turnover besides glycemia, little is known about the physiological and pathological conditions affecting GA levels. This study was aimed to prove the effects of body mass index (BMI) on GA measurement in diabetic patients. We studied 209 patients with type 2 diabetes mellitus whose HbA_1c levels had been stable for at least the past three months. In the study patients HbA_1c and GA levels were found to be correlated to one another. Fasting plasma glucose (FPG) was significantly correlated with HbA_1c and GA. BMI showed a significant negative correlation with GA levels, whereas there was no correlation of BMI with HbA_1c levels. Multivariate regression analyses revealed that only FPG was positively correlated with HbA_1c, while FPG was positively and BMI was negatively correlated with GA. Only BMI was negatively correlated with the ratio of GA to HbA_1c. These results clearly demonstrate that GA levels are negatively influenced by BMI in diabetic patients.