The thromboresistance of some copolypeptides prepared from four amino acids, glycine(Gly), alanine(Ala), proline(Pro) and γ-benzyl-L-glutamate (γBLG), was investigated. The influencing factors on thromboresistance such as critical surface tension (γ_c) and clotting time were measured. In Gly-Ala copolypeptide, γ_c determined from the contact angle measurements was found to increase as the α-helical content increased. To examine the blood compatibility of the copolypeptides clotting time determined according to the Lee-White methods decreased with decreasing optical rotatory dispersion, and with the increase in proline content in Ala-Procopolypeptides. This decrease was thought to result from the adsorption of plasma protein to carbonyl bond which doesn''t have hydrogen bond in poly-L-proline. In Gly-γBLG copolymer clotting time was found to increase as the glycine content increased, whereas critical surface tension increased as the γBLG content increased. Discussions of the influence of hydrophobicity on the thromboresistance was made.