Background: To investigate the efficacy of intraconary tirofiban during primary percutaneous coronary intervention (PCI) for patients with acute coronary syndrome (ACS).Methods and Results: 118 patients aged 70 years and above (average age 75±2) were divided into study (n=58, intracoronary bolus tirofiban) and control (n=57, intravenous tirofiban) groups. The culprit vessels were targeted with primary PCI in all patients. Compared with the control group, the study group showed better TIMI flow grades and TMI myocardial perfusion grades (TMPG) immediately after PCI (P=0.016 and 0.026, respectively). The 14-day composite major adverse cardiac event (MACE) rate was lower in the study group (3.5% vs 17.5%, P=0.030) but it was similar between the two groups at 30 days following PCI (7.0% vs 1.7%, P=0.350). The left ventricular ejection fraction in the study group was higher than in the control group 30 days following the PCI (67.4±6.2% vs 60.7±4.6%, P=0.033). The 14-day bleeding complication (P=0.201) and platelet reduction rates (P=0.984) were similar between the two groups.Conclusion: In patients with ACS undergoing primary PCI, intracoronary bolus tirofiban administration is superior to intravenous bolus injection in improving coronary flow, myocardial perfusion and short-term clinical outcomes.