Surface modification of polypropylene hollow fiber membranes was peformed in order to develop blood-compatible biomaterials for use in the blood contacting and oxygenation membranes of a lung-assist device(LAD). Blood compatibility was determined by using anticoagulation blood and evaluating formation of blood clots on their surfaces as well as activation of plasma coagulation cascade, platelet adhesion, and aggregation. It was verified that the number of platelets on the silicone coated fibers was significantly lower than those on polypropylene. It was also found that the polypropylene hollow fiber membranes using plasma treatment exhibited suppression of complement activation in blood compatibility test.