Amphiphilic triblock copolymer (Pluronic F127) was used as a macromolecular additive to modify the surface of poly(ether imide) (PEI) ultrafiltration (UF) membranes with additive contents from 0 to 3 wt % in the casting solution. The surface modification of the membranes was confirmed by Fourier transform infrared spectroscopy and contact angle measurements. The membranes were also characterized by scanning electron microscopy, UF of proteins, and flux recovery. A membrane with the highest Pluronic (3 wt %) in PEI exhibited the highest pure water flux, highest water content, and lowest membrane hydraulic resistance. It exhibited high UF fluxes of 170 and 180 L m(2) h(1) at 345 kPa, for 1.0 g/L bovine serum albumin (BSA) in phosphate buffer solution and 1.0 g/L humic acid (HA) in deionized water feed solutions, with solute rejections of 84 and 82%, respectively. It also showed that the blended membranes with 3 wt % Pluronic content had a higher flux recovery ratio (92.4 and 89.4%), slightly higher reversible fouling (25.8 and 18.8%), and lower irreversible fouling (7.6 and 10.6%) after the UF of BSA and HA solute separation. This explained their low fouling behaviors compared to the neat PEI membranes.