Objective The aim of this study was to investigate the role of the urinary chiro- and myo-inositol levels in predicting type 2 diabetes mellitus. Methods 103 normal controls and 111 type 2 diabetic patients were enrolled in this study. The concentrations of urinary chiro- and myo-inositol were measured by high performance liquid chromatography/mass spectrometry. Results The concentration of urinary chiro-inositol in diabetic subjects (1.86±2.64 ng/L) was significantly higher than in controls (0.44±0.42 ng/L)(p＜0.001). The urinary myo-inositol level in diabetic subjects (40.59 ±39.09 ng/L) was also significantly higher than in controls (14.13±10.31 ng/L)(p＜0.001). The urinary chiro-inositol multiplied by myo-inositol level in diabetic subjects (103.69±185.11) was significantly higher than in controls (8.26±13.26)(p＜0.001). The cutoff value to predict type 2 diabetes mellitus was 0.40 ng/L (sensitivity 65.8%, specificity 65.0%) for chiro-inositol and 17.10 ng/L (sensitivity 66.0%, specificity 65.8%) for myo-inositol. The cutoff value for chiro- times myo-inositol to predict type 2 diabetes mellitus was 7.43 (sensitivity 70.0%, specificity 70.3%). The area under the receiver operating characteristic (ROC) curve (95% CI) to predict type 2 diabetic mellitus was 0.712 (0.636-0.787) for chiro-inositol and 0.690(0.611-0.769) for myo-inostiol. The area under the receiver operating characteristic (ROC) curve (95% CI) for chiro-inositol multiplied by myo-inostiol to predict type 2 diabetic mellitus was 0.746(0.674-0.819). Conclusion The urinary chiro- and myo-inositol levels were increased in type 2 diabetic patients and urinary chiro-inositol multiplied by myo-inositol was sufficient marker to predict type 2 diabetes mellitus.