Background: Near complete inhibition of platelet aggregation, achieved with aspirin, clopidogrel loading and Gp IIb/IIIa inhibitor has been known to decrease the major adverse cardiac events (MACE) in patients with acute coronary syndrome and STEMI. But, few data are available for the early use of co-administered Gp IIb/IIIa inhibitor with clopidogrel loading dose 600 mg for STEMI. This study tried to investigate the beneficial role of upstream glycoprotein(Gp) IIb/IIIa inhibitor (Clotinab, ISU ABXIS, Seoul) with 600 mg clopidogrel pretreatment would have a better tissue-level perfusion and improved clinical outcomes in ST elevation myocardial infarction (STEMI). Methods: A total statin naïve 761 patients with STEMI among 914 patients were randomized to upstream use with Clotinab at emergency room [group 1: n=378] or only bail out use during the percutaneous coronary intervention (PCI) [group 2: n=383]. All patients were prescribed a clopidogrel 600-mg before primary PCI. The primary end-point of this study was a 30-day incidence of MACE including death, non-fatal MI, target vessel revascularization and stroke. Results: The MACE occurred in 34 patients (9.0 %) in group 1 and 41 patients (11.0 %) in group2, which was not significantly different (p=0.47). But, the incidence of major and minor bleeding was significantly higher in group 1 [14 (4.0 %) vs. 4 (1.0 %), p =0.01]. Secondary end-point including TIMI grade, ST resolution at 90 minutes, corrected TIMI were no significantly different between 2 groups. Conclusions: The upstream use of Gp IIb/IIa inhibitor under the 600 mg clopidogrel loading not decrease the MACE and improve the coronary flow after primary PCI. Therefore, upstream use of Gp IIb/IIIa inhibitor could not be helpful in all patients with STEMI but only selected patients during the PCI.