The PVC-g-MnG polymers were synthesized by photo-induced graft copolymerization of methoxypoly (ethyleneoxide)monomethacrylate (MnG) with various chain lengths (n) of polyethyleneoxide (PEO) (n = 4, 9, 15, 23, 50, 100) as side chains to polyvinylchloride (PVC) with photo-sensitive dithiocarbamate groups. Antithrombogenicity has been evaluated in vitro and in vivo. The in vitro and in vivo results indicated that the adsorption of blood elements to the PVC-g-MnG significantly decreased with the increasing PEO chain length (n). From these findings it is suggested that the volume restriction effect resulted from the formation of long-chain PEO on the surface and which effectively suppresses the adsorption of blood elements and prevents the denaturation of blood elements.