Objectives: Myocardial perfusion scintigraphy(MPS) is a valuable tool for the detection and localization of coronary artery disease (CAD). Its diagnostic accuracy is limited by irregular body photon attenuation. The aim of this study is to compare atenuation correction (AC) with non-AC (NC) on the distribution of myocardial perfusion, and to evaluate the quantitative effect of using AC on MPS for the assessment of CAD. Methods: Thirty-nine patients undergoing dual-isotope ECG-gating MPS were included. Resting imaging was performed 5 min after administration of 74 MBq TI-201. Persantin-induced stress study was performed 30 min after injection of 1110 MBq Tc-99m MIBI. All images were acquired with a dual-head gamma camera (Siemens ECAM), equipped with two scanning Gd-153 line sources. lmaqes were reconstructed using iterative maximum-likelihood algorithm with and without AC. The perfusion percentage from the five individual walls of anterior wall, septum, inferior wall, lateral wall and apex, defect extent and defect severity were calculated, respectively. The myocardial perfusion between AC and NC studies was analyzed by using a paired t test. The significanc level was set at P<0.05. Results:Twenty of the 39 patients were proven of no evidence of CAD or restenosis (Group 1),while the rest 19 patients were documented of CAD (Group 2). Among the five individual walls in Group 1 patients ,the perfusion percentage was changed greatest in the inferior wall after AC, which increased 13.0+ 5.2% on rest TI-201 and 13.6 + 5.8% on stress Tc-99m MIBI images, respectively (P<0.001). In Group 2 patients, the defect extent changed from 19.6 + 13.2% to 14.9 + 12.1% (P<0.01) on rest TI-201 and 23.2 + 13.6% to 20.7 + 11.5% on stress Tc-99m MIBIimages (p=0.055) after AC. The defect severity of the myocardium changed from 15.6 + 10% to 7.6 + 8.1% (P<0.001)on rest TI-201 and 18.4 + 10.5% to 15.6 + 7.6% (P<0.05) on stress Tc-99m MIBI images after AC. Conclusion: AC significantly corrects the myocardial perfusion for patients without CAD,thereby reducing the possiblity of false-positive results. AC could also change the defect extent and defect severity for patients with CAD, and help to precisely clarify the area of myocardial abnormality.