Objective: To survey the prevalence of nonresponse to aspirin, clopidogrel in patients with percutaneous coronary intervention. Methods: A cross-sectional study was conducted at the Heart Institute in Ho Chi Minh city from 12/2011 to 6/2012 on patients with percutaneous coronary intervention. Two anti platelet agents with a loading dose of 600 mg clopidogrel and 325 mg aspirin were used for patient with acute coronary syndrome before undergoing urgent intervention. Patients with chronic coronary artery disease received the dose of 100 mg aspirin and 75 mg clopidogrel/day at least 4 days before undergoing scheduled angioplasty. After the intervention, all patients take aspirin 250 mg/day and clopidogrel 75 mg/day. Platelet function were measured about 48 hours after the intervention with PFA 100 (Platelet Function Analyzer 100) with cartridge collagen/epinephrine (CEPI) for aspirin and INNOVANCE P2Y forclopidogrel nonresponse. Results: In 174 patients enrolled in the study, the prevalence of nonresponse to aspirin, clopidogrel were 21.3 percent and 26.4 percent. Conclusion: Prevalence of anti platelet therapy nonresponse is higher in patients undergoing percutaneous coronary intervention.