Aim: To purify and characterize the coagulant protein FIa from Daboia russelli siamensis (Myanmar) venom. Methods: FIa was purified from Daboia russellisiamensis (Myanmar) venom by ion-exchange chromatography on CM-Sephadex C-50, and gel filtration on Sephadex G-75 and a Superdex 75 column. The hemostatic activity of FIa was determined by the method of Williams and Esnouf. The specific chromogenic substrates were used respectively to determine the activation of factor X and prothrombin. The fibrinogen-clotting activity of FIa was determined by the method of Gao et al. Normal saline was used as a negative control while factor Xa and thrombin were used as positive controls, respectively.Results: FIa, a coagulant protein, was achieved by ion-exchange chromatogra-phy and gel filtration with a molecular weight of 34 479 and an isoelectric point of 7.2. FIa was shown to have strong hemostatic activity. The hemostatic activity of 0.5 mg FIa was equal to that of 1.5625 u thrombin. FIa primarily activated factor X,however, had no influence on prothromhin, nor did it cleave or clot fibrinogen.Conclusion: FIa is a factor X-activating enzyme, which could activate factor X to factor Xa, but has no effect on prothrombin and fibrinogen.