BACKGROUND: Among cardiovascular risk factors, apolipoprotein B/apoA1 ratio is considered to have the strongest predictive value for cardiovascular outcomes. Also apolipoprotein B/apoA1 ratio is marker of the balance between proatherogenic and antiatherogenic lipoprotein particles. However, little data are available about the relationship between apolipoprotein B/apoA1 ratio and plaque components. OBJECTIVES: We used virtual histology-intravascular ultrasound (VH-IVUS) to evaluate the relationship between apolipoprotein B/apoA1 ratio and plaque components in patients with coronary artery disease. METHODS: We divided the patients into three groups according to the apolipoprotein B/A1 ratio: Group I [ApoB/A1 ratio < 0.75 (n=272)]; Group II [ApoB/A1 ratio = 0.75 - 1.1 (n=198)]; Group 珪 [ApoB/A1 ratio > 1.1 (n=47)]. VH-IVUS analysis classified the color-coded tissue into four major components: fibrotic; fibro-fatty; dense calcium (DC); and necrotic core (NC). RESULTS: Group 珪 had highest total cholesterol (165짹34 vs. 204짹35 vs. 231짹44 mg/dl, p<0.001) and low-density lipoprotein cholesterol (99짹28 vs. 139짹27 vs. 166짹35 mg/dl, p<0.001), and had lowest high-density lipoprotein cholesterol (53짹13 vs. 46짹26 vs. 39짹8 mg/dl, p<0.001). At the minimum lumen site, Group 珪 had smallest lumen cross sectional area (5.6짹3.3 mm2 vs. 4.9짹2.7 mm2 vs. 4.7짹2.3 mm2, p=0.027), and had greatest plaque burden and absolute NC area (64짹13% vs. 67짹11% vs. 68짹11%, p=0.011, and 1.3짹1.1 mm2 vs. 1.5짹1.0 mm2 vs. 1.8짹1.3 mm2, p=0.017, respectively). At the largest NC site, Group 珪 had greatest plaque burden (61짹12% vs. 64짹10% vs. 65짹12%, p=0.005), and absolute NC area and percent NC area (1.8짹1.2 mm2 vs. 2.1짹1.2 mm2 vs. 2.4짹1.2 mm2, p=0.002, and 26.4짹11.4% vs. 28.7짹10.8% vs. 29.8짹10.5%, p=0.035, respectively). The absolute DC and NC volumes and percent NC volume were greatest in Group 珪 (11.4짹13.4 mm3 vs. 13.8짹13.0 mm3 vs. 16.6짹12.0 mm3, p=0.019, and 17.6짹17.2 mm3 vs. 24.9짹21.9 mm3 vs. 31.5짹22.6 mm3, p<0.001, and 17.8짹9.0% vs. 19.7짹8.9% vs. 21.9짹9.7%, p=0.004, respectively). The absolute plaque and NC volumes and the percent NC volumes positively correlated with apolipoprotein B/A1 ratio (r=0.167, p<0.001, r=0.180, p<0.001, r=0.098, p=0.026, respectively). CONCLUSIONS: VH-IVUS analysis demonstrates the association between apolipoprotein B/A1 ratio and vulnerable plaque components in patients with coronary artery disease.