To understand the effects of protein adsorption on filtration performance, poly(a-hydroxyethyl methacrylate) (PHEMA) was grafted by the gamma -ray preirradiation process onto the porous surface of a polypropylene (PP) membrane. The colloidal filtration of such membranes was discussed with respect to the correlation between the adsorption of the bovine serum albumin (BSA) proteins and the variation of physical properties of the PP-graft-PHEMA (PP-g-PHEMA) membrane surface. The specific resistance (alpha (c)) of the protein layer formed during filtration was obtained by line fitting through the filtration experimental results, using the colloidal filtration model proposed by Carman. The existence of PHEMA gave much faster rates of permeation than those of the original PP membrane because of the more or less dilute BSA protein concentration at the PHEMA layer. It was confirmed from the filtration experiment that the PHEMA layer grafted on the surface of the membrane prevented the intimate contact of BSA proteins with the surface of the membrane, resulting in a low specific resistance because of the increase of interspacing of the protein layer composed of the BSA protein particles. Especially, alpha (c) of a 40.6 wt % PHEMA layer is 0.72 x 10(2) (m(-1) g(-1)), much lower than that of the unmodified original PP membrane (alpha (c) = 6.24 x 10(2)). In addition, although the mutual repulsive interaction between BSA protein and the surface of the PP-g-PHEMA membrane was weak with the increase of the grafting degree, the low adsorption of BSA proteins with the increase of PHEMA grafting was crucially affected by the contribution of the higher roughness and hydrophilicity due to grafting PHEMA rather than by the contribution of repulsive interaction between two species.