Background Antiplatelet resistance has been proposed as a possible mechanism to explain recurrent cardiovascular events in patients who have coronary artery disease and who are undergoing dual antiplatelet therapy. This study was to identify possible risk factors associated with a lack of response to clopidogrel treatment in patients with coronary artery disease. Method Between Jaunuary and August 2011, 106 coronary artery disease patients (78 male; mean age=62.0짹11.9) were included. All patients were given loading doses or maintenance doses for more than 7 days of aspirin and clopidogrel before coronary intervention. The P2Y12 reaction unit (PRU) measured with the VerifyNow P2Y12 assay (Accumetrics, San Diego, California) at 4 days after coronary intervention. Clopidogrel resistance was defined as P2Y12 reaction unit (PRU) >252 according to the result of CILON-T study. Result The rate of clopidogrel resistance was 26.4%. In univariate analysis, age, hemoglobin, hematocrit, hypertension, smoking, total cholesterol, body weight had a significant association with clopidogrel resistance. The values of PRU were well correlated with the level of hemoglobin (r=-0.446, p<0.0001, figure), however were not correlated with parameters of platelet count and functions, inflammation and ventricular loading. Based on multivariate analysis, hemoglobin (odds ratio [OR], 0.625; 95% confidence interval [CI], 0.420-0.929; p=0.02) and hypertension (OR, 4.488; 95% CI, 1.227-16.419; p=0.023) were shown to be an independent predictor of clopidogrel resistance after adjusting for confounding variables. Conclusion The result of this study suggests that blood hemoglobin level and hypertension in clopidogrel users affect the platelet response to these treatments.