Background: This study evaluated the effect of omeprazole or pantoprazole on platelet reactivity in non-STsegment elevation acute coronary syndrome(NSTE-ACS) patients receiving clopidogrel.Methods: Consecutive patients with NSTE-ACS(n =620) from general hospital of Shenyang Military Command were randomized to the omeprazole or pantoprazole(20mg/d) group(1:1), and received routine dual antiplatelet treatment. Patients’ reversion rate of adenosine diphosphate-induced platelet aggregation(ADP-PA) was assessed at baseline, 12 to 24 h after administration of medication, and after 72 h of percutaneous coronary intervention(PCI). The primary endpoint of the study was platelet reactivity assessed with ADP-PA at 30 days after PCI. Adverse events(AEs) were recorded for 30-day and 180-day follow-up periods.Results: There were no significant differences between both the groups in platelet response to clopidogrel at 12–24h after drug administration(54.09%±18.90% vs. 51.62%±19.85%, P=0.12), 72 h after PCI(52.15%±19.45% vs. 49.66%±20.05%, P=0.18), and 30 days after PCI(50.44%±14.54% vs. 48.52%±15.08%, P=0.17). The rate of AEs did not differ significantly between groups during the 30-day(15.2% vs. 14.8%, P=0.91) and 180-day(16.5% vs. 14.5%, P=0.50) follow-up periods after PCI.Conclusion: The addition of omeprazole or pantoprazole to clopidogrel did not restrict the effect of platelet aggregation by reducing the conversion of clopidogrel. Compared with clopidogrel alone, pantoprazole-clopidogrel and omeprazoleclopidogrel combinations did not increase the incidence of adverse clinical events during 30-day and 180-day follow-up periods after PCI. Background: This study evaluated the effect of omeprazole or pantoprazole on platelet reactivity in non-ST segment elevation acute coronary syndrome (NSTE-ACS) patients receiving clopidogrel. Methods: Consecutive patients with NSTE-ACS (n = 620) from general hospital of Shenyang Military Patients were either randomized to the omeprazole or pantoprazole (20 mg / d) group (1: 1) and received routine dual antiplatelet treatment. Patients’ reversion rate of adenosine diphosphate-induced platelet aggregation (ADP- PA) was assessed at baseline, 12 to The primary endpoint of the study was platelet reactivity assessed with ADP-PA at 30 days after PCI. Adverse events (AEs) were recorded for 30-day and 180-day follow-up period. Results: There were no significant differences between both groups in platelet response to clopidogrel at 12-24h after drug administration (54.09% ± 18.90% vs. 51.62% ± 19.85%, P = 0.12) , 72 h after PCI (52.15% ± 19.45% vs. 49.66% ± 20.05%, P = 0.18) and 30 days after PCI (50.44% ± 14.54% vs. 48.52% ± 15.08%, P = 0.17). The rate of AEs did not differ significantly between groups during the 30-day follow-up periods after PCI-Conlusion: 15.2% vs. 14.8%, P = 0.91 and 180-day (16.5% vs. 14.5%, P = 0.50) Compared with clopidogrel alone, pantoprazole-clopidogrel and omeprazoleclopidogrel combinations did not increase the incidence of adverse clinical events during 30-day and 180-day follow- up periods after PCI.