Envenomation caused by Lonomia obliqua is a public health hazard in Southern Brazil. Envenomed victims present severe hemorrhagic syndrome that can progress to intracranial hemorrhage and death. To understand the mechanisms that lead to hemorrhage, we investigated the platelet dysfunction and blood coagulation disturbances following experimental envenomation in rats. L. obliqua bristle extract was injected (s.c.) and blood collected at different times post-venom administration for determination of platelet response and analysis of blood coagulation. Rats presented hypofibrinogenemia and platelet hypoaggregation in platelet rich plasma (PRP). After addition of exogenous fibrinogen to PRP, platelet hypoaggregation was not corrected. Interestingly, normoaggregation was observed when platelets were separated from plasma. In addition, incubation of plasma from envenomed rats inhibits aggregation response of normal washed platelets. These results indicate that an aggregation inhibitor is generated in plasma during envenomation. Moreover, rats presented an increase in nitric oxide plasmatic levels which coincided with maximum inhibition in platelet aggregation. Animals also showed blood incoagulability and a significant increase in thrombin, plasmin and urokinase plasmatic activities. Despite this intravascular thrombin generation, only a slight decrease in platelet numbers was detected. Certainly, the platelet hypoaggregation and blood incoagulability described herein contribute to systemic bleeding observed in patients.