【Abstract】 Object To probe the possibility of bioelectrical impedance vector analysis (BIVA) as a tool to estimate dry weight (DW) in maintenance hemodialysis patients. Methods Maintenance hemodialysis patients with adequate DW appreciated based on clinical experience in the Hemodialysis Center of Peking University First Hospital were included in this study. Single frequency (50kHz) and whole-body impedance vector were measured before and after hemodialysis (HD) sessions. Vector distribution was compared with that of healthy subjects living in the Shijingshan District in Peking. The 95% confidence ellipses for MHD patients and healthy subjects and the tolerance ellipses for healthy subjects were drawn on the resistance-reactance vector graph. Before HD session, the patients were divided into group A (overhydration) and group B (normohydration) according to their vector tolerance analysis, and the occurrence of hypertension was compared between the two groups. After HD session, the patients were divided into overhydration, normohydration and dehydration groups according to their vector tolerance analysis. The prediction of DW adjustment was then made based on hydration status, and their blood pressure levels before and after HD session were compared. Results In this study, 290 healthy subjects (male : female = 149:141) and 37 adult maintenance hemodialysis patients (male : female = 13:24) were included. Compared with those of healthy subjects, the vector was shorter and the phase angle was smaller in patients before HD, and the vector became longer and the phase angle became larger after HD. The vector displacement after HD indicates the improvement of hydration status in patients. Before HD, hypertension was found in 39.3% patients in group A, and in 22.2% patients in group B. Blood pressure was lower in dehydration group than in overhydration and normohydration groups, but the differences had no statistical significance. The consistent rate between DW assessed by BIVA and that by clinical assessment was 70.3%. By BIVA, 11 patients were suggested to have DW readjusted. After observation for 2 weeks, DW was readjusted with the same direction based on BIVA prediction in 5 of the 11 patients. Conclusions Before HD, overhydration prevailed even in patients with adequate DW. BIVA is useful for the assessment of inadequate DW earlier than the presence of clinical symptoms, and is thus a helpful method for physicians to evaluate DW in maintenance hemodialysis patients.