Abstract： Background Optical coherence tomography (OCT)is a new imaging modality with resolution of approximately 10 μm and can be employed to visualize intracoronary characteristics.Sirolimus-eluting stents(SES)are susceptible to late thrombosis due to delayed re-endothelialization over the stent struts,which may result in acute myocardial infarction or death.This study was designed to evaluate the re-endothelialization and neointimal coverage of SES with OCT 6 months and 12 months after implantation.Methods A total of 36 patients enrolled in the study underwent OCT examination 6 months(17 patients)and 12 months (19 patients)after SES implantation.The strut apposition to the vessel wall and neointimal coverage on SES struts were evaluated by OCT.Results Forty-six SES and 6561 struts were analyzed.At 6 months,3041 struts(98.7%)were well-apposed and 39 struts(1.3%)were malapposed.At 12 months,3434 struts(98.6%)were well-apposed and 47 struts(1.4%)were malapposed.Furthermore,only 4 SES at 6 months(18.2%)and 10 SES at 12 months(41.7%)were fully covered by neointimal growth.The average neointimal thicknesses covering the analyzed struts at 6 months and 12 months were (42±28)μm and (88±32) μm,respectively.There were 1989 struts at 6 months(72.1%)and 1461 struts at 12 months (45.6%)with neointimal thickness ＜100 μm.Conclusions OCT was able to visualize the strut apposition to the vessel wall and neointimal coverage on SES struts.At 6-month and 12-month follow-up examinations most struts were covered with thin neointima,but few of the entire SES showed full coverage.To prevent late-stent thrombosis in the presence of uncovered stent struts,longer dual antiplatelet drugs therapy should be recommended.