Background : Bifurcation lesion has been known as a predictor of late stent thrombosis(LST) which is a life-threatening complication of drug-eluting stents(DES). However, the cause of LST in bifurcation lesion remains unclear. Methods : From September 2007 to May 2009, OCT images were acquired in 51 patients(32 men and 19 women) at 7-12months of follow up after DES implantation crossed over a side branch. The covered and uncovered groups were divided according to complete neointimal coverage of unopposed struts in a side branch. The sirolimus-eluting stent(SES) group consisted of 24 stents in 22 patients, the paclitaxel-eluting stent(PES) group consisted of 16 stents in 15 patients, and the zotarolimus-eluting stent(ZES) group consisted of 16 stents in 14 patients. The strut coverage, mean neointimal thicknesses(NIT) and neointima area for DES groups were measured. Results : Significant differences between covered and uncovered groups(p=0.011) were observed according to types of DES. In ZES group, neointimal coverage of struts was significantly different from other two groups(83% of 143 struts, 20% of 165 struts and 65% of 356 struts, in the ZES, PES and SES groups, respectively; p<0.001). Also, the mean NIT in the PES group was significantly less than that of the ZES and SES groups(0.02짹0.02mm, 0.08짹0.06mm and 0.04짹0.03mm, in the PES, ZES and SES groups, respectively; p=0.002). Conclusions : In the present study, significant differences of stent strut coverage crossing a side branch in bifurcation lesion were observed according to DES types. This result suggests that DES do not cause the same degree of endothelialization in bifurcation lesion. These findings may explain the risk of LST after DES implantation in bifurcation lesion. Keywords : neointimal coverage, bifurcation lesion, drug eluting stent