Background: Some studies have reported that aspirin resistance was associated with myocardial infarction, stroke, myonecrosis after percutaneous coronary intervention. However, aspirin resistance and its clinical implication in patients undergoing drug-eluting stent (DES) implantation were not sufficiently evaluated. Methods: Four hundred nineteen consecutive patients who underwent DES implantation were enrolled. All of the patients took aspirin 100 mg (228 patients, 54.4%) or 200 mg (191 patients, 45.6%). Aspirin resistance was measured using the Ultegra Rapid Platelet Function Assay-ASA (Accumetrics, San Diego, Calif, USA). Aspirin resistance was defined as aspirin reaction unit (ARU) ��� 550. We followed up all patients for 9 months. Results: Aspirin resistance was founded in 33 patients (33/419, 7.9%). Aspirin doses (118.18 짹 39.2 mg vs. 147.93 짹 50.0 mg, p = 0.011) was lower in aspirin resistant (n=33) versus aspirin sensitive group (n=386). There were no significant differences in occurrence of myocardial necrosis (15.6% vs. 15.5%, p = 0.988). On multivariate analysis, low-dose aspirin (odds ratio 4.714; 95% CI 1.865 ~ 11.914; p = 0.001), age (OR 1.048; 95% CI 1.005 ~ 0.092, p = 0.029), platelet count (OR 1.007; 95% CI 1.001 ~ 1.014, p = 0.011), and hypercholesterolemia (OR 2.937; 95% CI 1.310 ~ 6.583, p = 0.009) were independent predictor of aspirin resistance. During 9 months, stent thrombosis and death did not occur, one acute myocardial infarction developed in aspirin sensitive group. Conclusions: Low-dose aspirin, old age, higher platelet count, and hypercholestrolemia were associated with high incidence of aspirin resistance in patients who underwent DES implantation. However, there were no significant differences in clinical outcomes between aspirin resistant and sensitive group during 9 month follow-up.