In some medical use, surface property such as biocompatibility and blood compatibility is very important. To improve the surface property of polymers, ammonia plasma was used to introduce amino group onto polymer surface in order to bind with heparin. The amount and the selectivity of amino group were improved by plasma treatment. The ratio of sulfur contained in heparin to carbon also increased from 0.5% to 10% by plasma process. The positive correlation can be found between heparin immobilization and amino group introduced by plasma. The immobilized heparin is strongly connected and it enhances the anticoagulant property on the surface.