The purpose of the present invention is to provide: a copolymer that is capable of being immobilized on a base material while maintaining a high antithrombotic property persistently without having to introduce heparin or an anticoagulant drug to the surface thereof and a medical material using same. Provided is a copolymer that comprises monomer unit A, monomer unit B, and monomer unit C represented in in chemical formula 1, wherein monomer unit C has a mole fraction of 0.5-40% with respect to the total amount of all constituent monomer units.本發明的目的在於提供一種共聚物,不用將肝素或抗凝血劑導入於表面,可持續且維持高抗血栓性的狀態固定於基材;及使用其之醫療材料。本發明提供一種共聚物,其係包含以下作為代表的單體單元A、單體單元B及單體單元C,且相對於構成的全部單體單元之該單體單元C的莫耳分率為0.5~40%。
