Objective：To assess the hemocompatibility of biomaterial covalently coated by chitosan／heparin designed for the closure of congenital heart defects in vitro. Methods：Chitosan（Chi）／heparin（Hep） was covalently immobilized onto the surface of Nitinol slices. The hemocompatibility of biomaterials was evaluated by using the hemolysis test． Ａnticoagulant activity was studied in vitro in a dynamic model with whole blood, and partial thrombin time（APTT）, prothrombin time（PT）, fibrinogen time, thrombin time（TT） and D-Dimer respectively. Surface characterizations such as protein adsorption and platelet adhesion were performed by using scanning electron microscopy. Results：White blood count, red blood count and platelet count（PC） were all in normal range and there were no evident difference in each group. The hemolysis rates of biomaterials was all less than 5％. Chi／Hep did significantly prolong the APTT, PT, and TT． In addition, the APTT, PT, and TT in groups coated with different concentration of Hep showed no significant difference. The immobilization of Chi／Hep caused the protein adsorption, platelet adhesion, and thrombus formation were all reduced by the immobilization of Hep. Conclusion：In vitro hemocompatibility of biomaterials designed for the closure of congenital heart defects can be improved by conjugating Chi／Hep onto the surface.