Both aspirin and vicagrel are effective antiplatelet drugs, with the potential for concomitant use as another dual-antiplatelet therapy for the prevention of recurrent thrombotic or ischemic events. Because they both are the substrates of carboxylesterase 2 (CES2), aspirin attenuated the metabolic activation of and platelet response to vicagrel in mice treated with the two drugs concomitantly. In this study, we sought to clarify whether vicagrel could affect platelet responses to aspirin and their underlying mechanisms. Plasma levels of aspirin and salicylic acid were determined by liquid chromatography-tandem mass spectrometry, inhibition of arachidonic acid (AA)-induced whole-blood platelet aggregation by aspirin was assessed with an aggregometer, and their antithrombotic effects were evaluated by arteriovenous shunt thrombosis model. The results showed that concomitant use of vicagrel (5, 10, or 20 mg/kg) led to an average of 55% and 77% increases in systemic exposure of aspirin (C_max and AUC_0-t) and 2.8-fold increase in suppression of AA-induced platelet aggregation in mice when compared with use of aspirin alone. In the rat thrombus formation model, vicagrel (1 mg/kg) enhanced inhibition of thrombosis formation by aspirin (5 mg/kg), but not vice versa. We conclude that vicagrel increases platelet responses to aspirin and also enhances inhibition of thrombus formation of aspirin due to decreased CES2-catalyzed aspirin inactivation in rodents, and that an integrated net effect on thrombus formation in vivo is superior to inhibition of AA- or ADP-induced platelet aggregation ex vivo by either of the two drugs if taken concomitantly.