Fibrinogen is an essential protein involved in several steps of hemostasis, being associated with the final steps of the blood coagulation mechanism. Herein, we describe the purification and characterization of a reptile fibrinogen, obtained from Bothrops jararaca plasma. Native B. jararaca fibrinogen showed a molecular mass of 372 kDa, and the reduced and alkylated fibrinogen molecule showed three chains of 71, 60 and 55 kDa, which are similar to the molecular masses of human and bovine Aalpha, Bbeta and gamma fibrinogen chains. Remarkably, B. jararaca fibrinogen was clotted by bovine thrombin, but B. jararaca, Crotalus durissus terrificus and Lachesis muta rhombeata venoms could not induce its clotting or hydrolysis. Thus, despite the similarities between B. jararaca and mammalian fibrinogens, the former shows distinctive features, which protect B. jararaca snakes from accidental envenomation.