Abstract: Objective To explore the inhibitory mechanism of fraction F of Naja naja atra venom on platelet aggregation. Methods Nephelometery was used to detect the effect of fraction F of Naja naja atra venom on platelet aggregation induced by adenosine diphosphate (ADP), arachidonic acid (AA) and platelet activating factor (PAF). The influence of fraction F of Naja naja atra venom on the binding of fluoreacenceconjugated monoclonal antibody CD41 (FITC-CD41) and CD61 (FITC-CD61) to membrane glycoprotein Ⅱb/Ⅲa (GPⅡb/Ⅲa) of platelet was measured by flow cytometry. Results Fraction F of Naja naja atra venom significantly inhibited the aggregation of platelet induced by ADP, AA and PAF in a dose-dependent manner. Fraction F of Naja naja atra venom obviously decreased the binding of FITC-CD41 to GPⅡb, and had no effect on the binding of FITC-CD61 to GPⅢa. Conclusion Fraction F of Naja naja atra venom can inhibit the platelet aggregation induced by different agonists, which is one of mechanisms underlying fraction F of Naja naja atra venom binding to GPⅡb/Ⅲa of platelet.