The purpose of the present invention is to provide an antithrombotic material which exhibits high antithrombotic activity that is sustained over a long period while reducing the thickness of the coating material. The present invention is an antithrombotic material comprising a coating material containing a compound having anionic anti clotting activity and including sulfur atoms together with a cationic polymer containing as a constituent monomer a compound selected from the group consisting of alkylene imine vinyl amine allyl amine lysine protamine and diallyl dimethyl ammonium chloride and a substrate having the surface thereof coated by said coating material wherein the cationic polymer is covalently bonded to the substrate and the compound having anionic anticoagulant activity and including sulfur atoms is immobilized on the substrate surface by ionic bonding with the cationic polymer and the average thickness of the coating material is 15 400nm.
