Background: There is a possibility of leakage (PVL; Paravalvular leak) flow around TAVI (Transcatheter Aortic Valve Implantation) and a high risk of thrombus formation. To find out the mechanism of thrombus formation by this leakage flow is important issue. In our previous studies, effects of the high shear rate on the thrombus formation rate at wall on orifice flow were examined by observation of thrombus formation using laser sheet, and it was found that the thrombus formation rates increase with the high shear rates. In this study, observation of thrombus formation around TAVI models including leakage flows by laser sheet in vitro with various geometries. Method: Experimental objects are orifice pipe flow and the leakage models with (Fig.1) for observation of thrombus formation. Each leakage size h is 0mm, 0.5mm, 1mm respectively with 20 mm diameter with stenosis to simulate valve part. The target flow filed with fresh blood plasma of pigs is observed with high speed CCD camera by laser sheet. Once the thrombus formation starts, the scattering wave can be detected by this system. The movies for three kinds of geometries and two flow rates (3 and 5l/min). Results & Conclusions: As for visualization results, typical distribution of thrombus formation area at h= 0, 0.5, 1 mm is shown in Fig.2. Due to the increasing of leakage size, the thrombus formation area at the outer wall decreases. In case of leakage size h=0.5 and 1 mm, these areas correspond to wake size at the back side of the stenosis. Figure 3 shows the thrombus formation rate by evaluation of the thrombus area with changing the leakage size and geometries. It was found that the thrombus formation rate increases with the leakage size, and there are differences between the two geometries. These findings related thrombus formation area were also evaluated from the leakage flow rates in the CFD (Computational Fluid Dynamics) results. And it was also found that this formation rates increase with leakage flow rate obtained by CFD. In conclusion, there is a high possibility to generate thrombus formation with larger leakage flow for TAVI. In future, the effects of valve motion should be investigated.