Random and block copolymers containing a phospholipid polar group in their side chain were synthesized by the copolymerization between 2-methacryloyloxyethyl phosphorylcholine and styrene. These copolymers showed amphiphilic character, especially poly(methacryloyloxyethyl phosphorylcholine-block-styrene) formed stable polymer micelles in water. The interaction between natural phospholipid, dipalmitoylphosphatidylcholine and methacryloyloxyethyl phosphorylcholine copolymers was investigated. The amount absorbed of dipalmitoylphosphatidylcholine from its liposomal solution on to the poly(methacryloyloxyethyl phosphorylcholine-co-styrene) surface increased with increase of methacryloyloxyethyl phosphorylcholine composition. Moreover, when poly(methacryloyloxyethyl phosphorylcholine-block-styrene) was added to dipalmitoylphosphatidylcholine solution, organization of dipalmitoylphosphatidylcholine molecules and stabilization of bilayer structure of dipalmitoylphosphatidylcholine liposome were found. This means that methacryloyloxyethyl phosphorylcholine moieties in the copolymer have a strong affinity to dipalmitoylphosphatidylcholine molecules. The blood compatibility of methacryloyloxyethyl phosphorylcholine copolymers was also investigated with particular attention to the aggregation ability of platelets after contacting methacryloyloxyethyl phosphorylcholine copolymers; this ability decreased when platelets were put in contact with polymers without a methacryloyloxyethyl phosphorylcholine moiety. On the other hand, aggregation ability remained at almost the same level to that of original platelets after contact with methacryloyloxyethyl phosphorylcholine copolymers. From these findings, we concluded that methacryloyloxyethyl phosphorylcholine copolymers show excellent blood compatibility due to adsorption of lipids from plasma and the formation of an organized adsorption layer of lipids on the surface of the methacryloyloxyethyl phosphorylcholine copolymers.