Computed tomographic coronary angiography (CTCA) can noninvasively identify calcified and noncalcified coronary plaques. The aim of this study was to compare the phenotypes of all plaques and of culprit plaques between patients with unstable angina pectoris (UAP) and those with stable angina pectoris (SAP), because plaque characteristics may differ between these patients. In 110 patients with UAP and 189 with SAP from a multicenter study comparing 64-slice CTCA with conventional coronary angiography, the number and phenotypes (noncalcified, mixed, and calcified) of coronary plaques were compared. In a subanalysis in 50 patients with UAP and 64 with SAP, culprit plaque characteristics, including culprit plaque cross-sectional area relative to total vessel cross-sectional area, culprit plaque length, remodeling index, and spotty calcification, were determined. Odds ratios for the presence of UAP, adjusted for clinical variables and the total number of plaques, were calculated for plaque characteristics on CTCA. Although the number of plaques was similar for patients with UAP and those with SAP, plaques in patients with UAP were more frequently noncalcified than in patients with SAP. The odds ratio for UAP was 1.3 (95% confidence interval [CI] 1.1 to 1.5) per noncalcified plaque. In the culprit plaque subanalysis, odds ratios for UAP were 0.99 (95% CI 0.96 to 1.01) per millimeter culprit plaque length, 2.7 (95% CI 1.2 to 6.4) for noncalcified culprit plaque, and 1.06 (95% CI 0.99 to 1.13) per percentage relative culprit plaque cross-sectional area. No significant relation was found between remodeling index or spotty calcification and UAP. In conclusion, noncalcified plaques and large noncalcified culprit plaques are more frequently found in patients with UAP than in those with SAP.