Purpose: Measuaring mean diameter and blood flow of arterio-venous fistula (AVF) in long duration hemodialysis. Material and method: From January 2005 to December 2005, at Thanh Nhan hospital, 31 long duration hemodialysis patients incluse: 17 men and 14 women, average aged: 48.7 years, average hemodialysis times: 3 years 2 months, have blood flow 250 ml/min in hemodialysis are treated to stabilize overload signs due to 3 degree congestive heart failure and affirmed by 2D ultrasound that they are lost dry weight accurrately before examined the AVF by Voluson 730 ProV color doppler ultrasound machine in order to obtain vascular ultrasound results more exactly. Result: Artery before the AVF about 5 cm: mean diameter = 5.6 + or - 1.2 mm, mean area = 26.4 + or - 11.0 mm2, thick wall = 0.75 + or - 0.2 mm, max velocity = 84 + or - 28.2 cm/s, min velocity = 52 + or - 21.9 cm/s, mean velocity = 64.8 + or - 25.7 cm/s mean blood flow = 1620,6 + or - 844 ml/min, PI = 0.54 + or - 0.2, RI = 0.4 + or - 0.1. At the AVF: mean diameter = 5.5 + or - 1.7 mm, mean area =26.0 + or - 15.6 mm2, max velocity = 98.9 + or - 24.4 cm/s, min velocity =55.3 + or - 18.5 cm/s, mean velocity = 71.3 + or - 20.8 cm/s, mean blood flow = 1869,4 + or - 1349,3 ml/min, PI = 0.58 + or - 0.17, RI = 0.43 + or - 0.13. Having a correlative between the diameter and blood flow of the artery before the AVF with diameter and blood flow at the AVF with R = 0.395, P = 0.02. Vein after the AVF about 5 cm: mean diameter = 9.4 + or - 3.0 mm, mean area = 76.4 + or - 144.9 mm2, wall thick = 0.7 + or - 0.4 mm, max velocity = 69.2 + or - 30.5 cm/s, min velocity =35.6 + or - 20.0 cm/s, mean velocity = 48.3 + or - 25.4 cm/s, mean blood flow = 3182.6 + or - 2159.2 ml/min, PI = 0.50 + or - 0.16, RI = 0.48 + or - 0.16. Having no correlative between the diameter arid arterial blood flow at the AVF with the diameter and blood flow of the vein after the AVF. Venous spectrum shape after the AVF (were arteriolisation: 30/31 patients, and were not arterialization: 1131 patients). Having no statistic signification difference between artery wall thick dimension before the AVF: 0.75 + or - 0.2 mm (0,7 0,8 mm) with arteriolisation venous wall thick dimenSion alter the AVF: 0.7 + or - 0.4 mm (0.5 - 0.8 mm). Conclusion: Vascular color doppler ultrasound measuare the blood flow and the dimension in end stage chronical renal patients and long duration hemodialysis patients may be prediced accurately the AVF to have adequate blood flow for hemodialysis.