Abstract: A pure crystalline hemostatic constituent has been isolated from Psidium Guava,and has been oomfirmed to be an ellagic acid by mp, UV, IR and R_f values, and its effect on the blood coagulation in rabbit has been investigated. By intravenous injection with a dosage of 20 mg/kg, it makes a 51% reduction in the average coagulation time of rabbit.