Left atrial appendage occlusion (LAAO) is a promising alternative for stroke risk reduction in patients with non-valvular atrial fibrillation who are not suitable for long-term oral anticoagulation (OAC). Current practice mandates use of post-procedural OAC for 45 days after WatchmanTM placement during which complete device endothelialization is expected to occur. However, most of the evidence supporting this strategy stem from animal studies. Incomplete device endothelialization are often encountered after 6-weeks of procedure and its therapeutic implications are less clear. Here, we present two cases of incomplete endothelialization after 1.5- and 2-year of Watchman implantation. In one of the cases, we believe that an eccentric mitral regurgitation jet caused shearing force on the Watchman device and impeded with normal endothelialization. In the other case, we found a device related thrombus possibly favored by prothrombotic environment created by lack of endothelialization. Further studies are warranted to find predictors and better diagnostic tool of LAAO endothelialization.