Abstract: Thrombolysis effect of recombinant staphylokinase (rSaK) developed in China was evaluated in rabbits with experimental pulmonary embolus model. ¹²⁵I-labeled human fibrin blood clot was prepared in vitro and was injected through jugular vein resulting in a pulmonary embolus. Twenty thousands AU·kg^-1(rSaK-H) or 5000 AU·kg^-1(rSaK-L) of rSaK was infused in 0.5 h at constant rate by a peristaltic 20000 U·kg^-1. Another 20000 AU·kg^-1 of rSaK was infused within 2.5 h(rSaK-2.5 h). The residual labeled blood clot in lungs were found to be 62%±11%(rSaK-H), 78%±7%(rSaK-L), 92%±7%(NS), 60%±13%(SK), and 64%±16%(rSaK-2.5 h).¹²⁵Ilabeled degradation products in blood and urine were also statistically higher in thrombolytic agents treated group than those in NS controls. The results suggest that the thrombolytic effect of rSaK was determined by total dose and not determined by infusion time. Two of seven rabbits in the rSaK 2.5 h infusion group, the bleeding time was prolonged to more than 10 minutes while no prolongation was seen in rSaK high dose group. The clot lysis curves were very similar in 0.5 h or 2.5 h treatment of rSAK in vitro. Michaelis-Menten kinetics studies in vitro revealed that the Kms of rSaK and SK were almost the same, while a higher maximal velocity(34 kBq·min^-1) was observed in rSaK than that in SK (10 kBq·min^-1).