Abstract: Objective TZDs is the medicine to decrease the blood glucose, but it has the side-effect of edema and water retention in body. In our research, we estimated the total body water （TBW） of patients with type 2 diabetes after different doses of treatment of Pioglitazone hydrochloride in 12 weeks. Methods In an open, controlled trial, 57 patients with type 2 diabetes who were under poor blood glucose control were enrolled. Additional Pioglitazone hydrochloride would be used combining with drugs used before, with a dose of 15 mg/d. After 4 weeks, Pioglitazone hydrochloride dose would increase to 30 mg/d if the fasting blood glucose could not match the goal （7.0 mmol/L）. Another 4 weeks, if the fasting blood glucose could not match the goal, Pioglitazone hydrochloride dose would increase to 45 mg/d. Fasting and 2 hours postprandial blood glucose, fasting blood lipid, glycosylated hemoglobin, hematocrit, body mass, electrocardiogram would be tested before and after treatment. Calculated BMI and estimated TBW by the Watson formula. Results Those subjects with type 2 diabetes who signed informed consent form were eligible for the cases（28 male and 29 female, aged from 25 to 69）. Among these 57 cases, 51 of them were efficient. By AVON analysis, we found that △TBW and △weight had significant differences among the 4 week, 8 week and 12 week groups, and showed the linear correlation. Compared to △TBW4 and △TBW8, △TBW12 significantly increased. TBW of males was higher than females. In female subjects, △TBW4, △TBW8 and △TBW12 showed the linear correlation, and △TBW12 of 30 mg/d groups and 45 mg/d groups were higher than △TBW4, but showed on difference in the male subjects. Conclusion With increasing dose of Pioglitazone hydrochloride and prolonging the treatment, TBW of patients with type 2 diabetes increased, especially for the female subjects.