Background��� Coronary computed tomography angiography (CCTA) has determined the severity of coronary artery lesions solely by visual plaque assessment. We investigated whether intraluminal attenuation gradients across lesion can augment detection of significant coronary artery stenosis by CCTA. Methods and Results��� From 64-detector row CCTA in 126 patients (100 male, age 61짹12 years) with obstructive coronary arteries, CCTA lumen cross-sectional area, mean diameter, and luminal attenuation (Hounsfield Unit, HU) of 370 major coronary arteries were evaluated by 5-mm intervals. Intervals with ���50% luminal diameter stenosis, significant calcifications, or stents were excluded due to non-linearity of intraluminal attenuation, and a total of 7,263 intervals were analyzed. Transluminal attenuation gradient (TAG), defined as the coefficient of linear regression between intraluminal attenuation (HU) and length (mm), of each vessel was compared to the stenosis evaluated by CCTA and also by invasive coronary angiography (CAG). TAG decreased consistently and significantly according to the severity of stenosis by CAG (diameter stenosis=0–49%, -2.34짹4.67 HU/10mm; 50–69%, -7.18짹6.91; 70–99%, -11.91짹7.61; 100%, -13.46짹9.59, p<0.0001 by ANOVA) as well as CCTA (0–49%, -1.91짹4.25 HU/10mm; 50–69%, -3.54짹4.43; 70–99%, -10.55짹7.20; 100%, -13.37짹9.81, p<0.0001). The diagnostic performance of CCTA could increase significantly after addition of TAG (N=370, c-statistic= 0.932짹0.012 versus 0.951짹0.010, p=0.001) and also in calcified plaque subgroup (N=127, c-statistic=0.825짹0.035 versus 0.880짹0.030, p<0.0001). Conclusion��� Transluminal attenuation gradient (TAG) is a novel method that can augment evaluation of the coronary artery stenosis by CCTA and can potentially discern vessel patency in cases of severe coronary calcification or complex coronary lesions.