Vulnerable plaques are characterized by large lipid cores, positive remodeling and small coronary calcium deposits. Multi-detector computed tomography (MDCT) has recently been shown to be able to characterize coronary artery plaques. The aim of this study was to evaluate culprit coronary lesions for differentiating acute coronary syndrome (ACS) from stable angina pectoris (SAP) using MDCT. 64-slice MDCT was conducted on 71 patients (ACS: 35, SAP: 36). The culprit coronary lesions were assessed according to the type and plaque attenuation (PA) of the plaque and the remodeling index (RI) as the ratio of the lesion and the reference area. The culprit lesion score (CLS) was defined as the sum of every score as 1.2 for a PA ≤ 60 Hounsfield units (HU), 1.1 for a RI ≥ 1.05 and 1.2 for a non-calcified or spotty calcification. More spotty calcification (95.0% vs. 23.1%, P < 0.001), a lower PA (40.17 ± 20.08 HU vs. 96.96 ± 58.19 HU, respectively, P < 0.001) and a higher RI (1.44 ± 0.43 vs. 0.90 ± 0.44, respectively, P < 0.001) were observed in the ACS patients. Also, the CLS of the ACS patients was significantly higher than that of the SAP patients (3.07 ± 0.63 vs. 1.18 ± 1.12, respectively, P < 0.001). A CLS more than 2.0 helped us to differentiate ACS from SAP with a sensitivity of 97.1% and a specificity of 67.6%. The CLS might be a useful tool for differentiating ACS from SAP.