In this study, poly(ethylene glycol) allylate[APEG] and sulphonated poly(ethylene glycol) allylate[APEG-S] was grafted onto cellulose acetate film in various grafting solution by a simultaneous irradiation grafting technique. The effect of various parameters such as APEG or APEG-S concentrations, adsorbed dose, and unitary or binary solvent systems on the grafting reaction was examined. For examination of blood compatibility of grafted cellulose acetate films, ACD human whole blood, platelet rich plasma(PRP), platelet poor plasma(PPP), and human plasma protein were used. The amount of thrombus formed on APEG and APEG-S grafted cellulose acetate films was evaluated by an in vitro method following Imai and Nose technique using ACD human whole blood. Human plasma protein was adsorbed onto APEG-S grafted cellulose acetate film surfaces, and the relative amount of proteins on the surfaces was evaluated by ESCA. The adsorbed protein and platelet adhesion on the grafted cellulose acetate film surface decreased markedly with the respect to control.