Inhibiton of the platelet glycoprotein IIb/IIIa receptor may reduce the incidence of adverse ischemic outcomes after percutaneous coronary intervention (PCI). We prospectively evaluated the long-term clinical effect of tirofiban after stent implantation in patients with acute coronary syndrome. A total of 60 patients (58.9+/-11.0 years; male:female=45:15) were randomly assigned to tirofiban with heparin (group I: 59.9+/-12.1 years; M:F=23:7; n=30) and heparin only (group II: 57.9+/-9.9 years; M:F=22:8; n=30). Clinical observation and follow-up angiography were completed at 6 months. The rates of major adverse cardiac events (MACE) and restenosis were compared during the follow-up period. Before and after PCI, the incidence of bleeding complication was not different between both groups. Twenty eight patients (group I; 13/30; group II; 15/30) underwent follow-up coronary angiography at six months after PCI. At six months, the group I showed a statistically decreased rate of primary composite end points, including cardiac death, myocardial infarction, and target lesion revascularization, compared with the group II (6.7% vs. 26.7%, p=0.038). Tirofiban, a platelet glycoprotein IIb/IIIa receptor blocker, can be used safely and effectively in patients with acute coronary syndrome.