Purpose: To compare the coronary CT angiography with Tc-99m sestamibi SPECT in detecting significant coronary artery disease. Materials and methods: Forty consecutive patients with clinically suspicious significant coronary artery stenosis ( Male : 21, Female: 19, Mean age: 60.5 years ) who underwent coronary CT angiography(CTA), Tc-99m sestamibi SPECT (MIBI) and conventional coronary angiography(CCA), were enrolled from 2003 January to 2004 December. CTA with 3D/2D reconstruction and MIBI including rest and pharmacologic stress images were taken. The coronary arteries of CTA and CCA were assessed for the presence or absence of a significant stenosis according to the AHA coronary artery segments. Side branches were included in the analysis of the respective main coronary artery (all 10 segments). Two radiologists evaluated the CTA in consensus and two specialists in the nuclear medicine department evaluated MIBI imaging data. Both the results were compared with those from the CCA. Results: In CCA, 29 out of 40 patients had significant coronary artery stenosis; 1 vessel disease:9, 2 vessel disease :13, 3vessel disease: 7, mild coronary artery obstructive disease:6, normal coronary artery:5. CTA correctly classified 25 out of 40 patients as having at least one significant coronary stenosis (sensitivity: 92.6%, specificity:84.6%, accuracy : 90 %) and MIBI correctly classified 17 out of 40 patients (sensitivity: 62.1%, specificity:81.8%, accuracy : 67.5 %). By analyzing each coronary territory, CTA correctly classified 44 out of 56 territories as having significant coronary stenosis (LAD/RCA/LCX territories- sensitivity: 92/76.5/57.1%, specificity:86.7/95.7/92.3%, accuracy: 90 /87.5/ 80 %, respectively) and MIBI correctly classified 28 out of 56 territories(LAD/RCA/LCX territories- sensitivity: 40/82.4/28.6%, specificity:86.7/91.3/100%, accuracy : 57.5 /87.5/ 75 %, respectively). CTA detected an addition of eight more significant stenosis to MIBI results but MIBI did only one. Conclusion: Compared to MIBI, CTA showed better localization of significant stenotic site, relatively higher accuracy. CTA is first recommended as a noninvasive examination in detecting significant coronary artery stenosis.