【Abstract】 Objectives To evaluate albumin loss during on-line hemodiafiltration (HDF) by using the new polysulfone high-flux membrane REXEED-15UC dialyzer. Methods An in vitro isovolemic online HDF model was established using bovine blood. REXEED-15UC dialyzer was used, and its effect was compared with that using HF-80S high-flux dialyzer. The experiment was divided into two groups: post-dilution HDF group (Quf=40mL/min and 60mL/min; N=3), and pre-dilution HDF group (Quf=80mL/min and 120mL/min; N=3). HDFwas lasted for 240 minutes and repeated for 3 times. Hemodiafiltrate fluid was taken out at different points (after 0, 1, 2, 4, 6, 8, 10, 20, 30, 40, 50, 60, 120, 180, and 240 minutes from the beginning of the experiment) during a single on-line HDF session. Albumin in hemodiafiltrate was measured by ELISA, and the total albumin loss in a HDF session was calculated using the area under the curve from the HDF using the REXEED-15UC dialyzer and HF-80S dialyzer. Results In the 2 groups using REXEED-15UC dialyzer or HF-80S dialyzer, albumin loss was less than 1.0g (0.261- 0.963g) in a single on-line HDF session. No statistical significance in albumin loss was found between the 2 doses used for post-dilution HDF group and pre-dilution HDF group in a single HDF session. In the two groups, the peak of albumin loss appeared in the first 10 minutes from beginning of the experiment. Conclusions REXEED-15UC dialyzer shows lower and clinically acceptable albumin loss in an on-line HDF session.