In this study, a novel nitric oxide (NO) endogenously releasing polyurethane (PU) material, i.e. PU-g-L-cysteine(PU-Cys), was synthesized by grafting L-cysteine on the film surface. Fluorescence analysis and a BCA method were used to characterize qualitatively and quantitatively the grafted L-cysteine. The results showed that L-cysteine was successfully immobilized on the PU film surface and the density of L-cysteine grafted was calculated to be 15.3nmol/cm2. The NO releasing behavior study of PU-Cys film demonstrated that endogenous NO could be continuously released from PU-Cys film and the accumulated releasing amount within 3h added up to 1.06nmol/cm2. The releasing rate of NO was well matchable to the self-releasing rate of resting platelets in human body. The results of dynamic blood clotting test and hemolysis ratio measurement showed that PU-Cys film had a better haemocompatibility than PU film, which might be the result of endogenously released NO inhibiting platelet adhesion and thrombus formation. Therefore, PU-Cys with the property of endogenous NO releasing is expected to be an ideal blood compatibility material in clinical application.