|Background/Aims: D-chiro-inositol is known as a mediator of insulin`s action and it has been shown to lower the blood glucose concentration in type 2 diabetes mellitus patient. This study aims to compare the urine D-chiro-inositol levels between normal controls and type 2 diabetes mellitus patients and we also searched for the relationship between the clinical characteristics of diabetes mellitus patients and the urine D-chiro-inositol concentration. Methods: 103 normal controls and 111 type 2 diabetes mellitus patients were recruited. Urine D-chiro-inositol was measured by the high performance liquid chromatography/mass spectrometry method. Results: Excretion of urinary D-chiro-inositol was increased in the diabetic subjects (p=0.000). In the diabetic group, the D-chiro-inositol level demonstrated a statistically significant positive correlation with HbA1c(r=0.264, p=0.007), microalbumin (r=0.252, p=0.021) and blood urea nitrogen (r=0.259, p=0.008) and it showed an inverse correlation with albumin (r=-0.198, p=0.045), ALT (r=-0.237, p=0.019) and the GFR (r=-0.200, p=0.043)(Table 2). Only the fasting plasma glucose level (ß=0.003, p=0.043) and the total cholesterol (ß=0.008, p=0.024) were found to be significant variables on the multiple regression analysis. When diabetic subjects were divided into two groups according to the HbA1c level, the subjects with a HbA1c level more than 8% presented a higher level of urinary D-chiro-inositol (p=0.019). Conclusions: The urinary D-chiro-inositol excretion of the diabetic subjects was increased. For the subjects whose HbA1c level exceeded more than 8%, the urinary excretion level of D-chiro-inositol was also increased. So we can expect more effectiveness of pinitol treatment in this poor glucose control group.