【Abstract】 Objective To investigate the relationship between blood flow in internal fistula (Qa) and vascular access function by measuring Qa and recirculation rate (R%) in internal fistula and following-up vascular access function in maintenance hemodialysis patients. Methods Qa and recirculation rate were measured 30 minutes after the initiation and one hour before the end of a hemodialysis session using the Transonic HD02 Monitor (Transonic Systems Inc). For the patients with lower or higher blood flow (Qa＜600 ml/min or >1, 800 ml/min), the possibility of vascular stenosis was evaluated by color Doppler ultrasonography to measure the diameters of internal fistula vessels including cephalic vein, radial artery and brachial artery, and the mean velocity of blood flow in the fistula. Vascular access function was carefully monitored in correlation to Qa. Results Vascular access function was successfully monitored in 125 patients, in which 3 cases (2.4%) were found to have recirculation rate >0%, Qa ＜600 ml/min in 32 patients (25.6%), Qa = 600-1800ml/min in 83 patients (66.4%), and Qa ＞1800ml/min in 10 patients (8%). The median Qa was 870 (565-1255)ml/min. In the 10 cases with lower Qa evaluated by color Doppler ultrasonography, 60-80% had abnormal vascular access function: stenosis at the anastomosis site was detected in 4 cases (40%), intima hyperplasia at the puncture site for many times in 2 cases (20%), venous shunt in 2 cases (20%), and patent fistula without detectable abnormalities in 2 cases (20%). In the 7 patients with higher Qa, all accompanied with radial artery dilatation. The inner diameters of cephalic vein and radial artery, and the velocity of blood flow in radial and brachial arteries were significantly different between patients with lower Qa and those with higher Qa. During the follow-up period of 36 months, vascular access occlusion resulting in another operation was found in 13 cases (40.6%) in the patients with lower Qa, and in 7 cases (8.4%) in the patients with normal Qa, but no case in patients with higher Qa. Correlation analysis indicated that Qa and the prognosis of vascular access were negatively correlated (r =-0.395, P＜0.001). Multiple regression analysis demonstrated that the Qa value influenced the prognosis of vascular access (β= -0.316, P=0.005). Conclusions Qa measurement by ultrasound dilution technology is useful for the prediction of vascular access prognosis in hemodialysis patients. The possibility of vascular access occlusion increases in patients with lower Qa. Therefore, Qa measurement is a valuable method for the evaluation of vascular access function either for autologous or for graft vascular access.