Background: The purpose of this study is to compare diagnostic power of CTCA with treadmill ECG test(TMT) in ambulatory patients and to determine the role of CTCA for the initial evaluation of chest pain on out-patient setting. Methods: We enrolled the 598 consecutive patients who mostly complaint chest pain and underwent the both TMT and CTCA for the evaluation of coronary artery disease (CAD) in out-patient clinics. Virtual triage to conventional coronary angiography(CCA) and revascularization treatment(RT), diagnostic accuracy of TMT and CTCA, positive rate among the patients group divided by risk factors(RF) include age(men ���45 yr, women ���55yr), Total cholesterol ���220 mg/dL, hypertension, current smoker and diabetes, positive rate of CTCA was analyzed and compared. Results: 120 patients with stenosis on CTCA and 115 patients with positive on TMT triaged to RT/CCA at 58/75(48/62%) and 23/41(20/35%), respectively (p<0.05). 302 patients with normal CTCA and 413 patients with negative on TMT triaged to RT/CCA at 1/6(0.8/5%) vs 27/51(6.5/12%), respectively (p<0.05). The proportion of not-interpretable patients on TMT was higher than those on CTCA (11.7% vs. 5%, p<0.05). Among 107 patients with CCA, kappa value of CCA and CTCA was 0.62 (p<0.001) and that of CCA and TMT was 0.145 (p=0.113). Sensitivity, specificity, positive predictive value (PPV) and NPV of CTCA were 89.9%, 74.0%, 90.6% and 71.4%, respectively and those of TMT were 50.0, 67.9, 78.0 and 37.3 respectively. PPV and NPV of TMT among the patients with non-significant and significant stenosis were 57.1 % and 91.7%, 86.7% and 10.0%, respectively. Positive rate of CTCA for coronary stenosis and not-significant plaques on any vessel were 6% and 20% of the patients with 1 RF, 26.4% and 51.2% of the patients with 2 RF, and 33.0% and 58.3% of the patients with above 3 RF. Conclusion: CTCA than TMT might be more effective as a first diagnostic tool for evaluation of chest pain in out-patients clinics and TMT might be helpful for detecting CAD among the patients with non-significant stenosis on CTCA