Background: Chronic total occlusion (CTO) lesion is a still a challenging issue for percutaneous coronary intervention (PCI) fields in terms of low success rate and high restenosis rate compared to other lesion subsets. We sought to evaluate in vivo tissue composition of CTO lesion, which is expected to have characteristics of complex lesion such as calcium. Methods: Study subjects consisted of 184 consecutive patients with stable angina, (mean 61.3짹11.0 years old, 124 male (67.4%)), who underwent PCI and intravascular ultrasound-virtual histology (IVUS-VH) examination. Volumetric IVUS-VH data was used after dividing by lesion length to compensate a difference of lesion length. Results: Patients who had CTO lesion (n=25, 20 males (80.0%), 60.8짹10.0 years old) being successfully treated with PCI had lower high-density lipoprotein cholesterol level (37.7짹7.1mg/dL vs. 44.8짹11.7mg/dL, p=0.005), higher creatinine level (1.83짹2.94mg/dL vs. 1.16짹0.96mg/dL, p=0.026), and lower left ventricular ejection fraction (58.8짹12.7% vs. 65.9짹9.4%, p=0.001) than those without CTO lesion (n=159, 104 males (65.4%), mean 61.411.1 years old). Gray scale IVUS data showed that CTO group had longer lesion length (23.9짹9.5mm vs. 17.0짹7.1mm, p<0.001), whereas no significant differences compared to those without CTO lesion in terms of plaque volume/length, vessel volume/length, remodeling index. IVUS-VH data showed that there was no significant difference between two groups in terms of volumetric tissue composition/lesion length and tissue composition at minimal luminal area site. Conclusion: The main finding of our study is that CTO lesion is a long lesion, but no specific difference in plaque composition compared with those in not CTO lesion. This may explain why the success rate of CTO lesion is increasing tendency despite of longer procedure time compared to not CTO lesion, although it was possible in part with recently developed guidewire and special technique.