Objective: To evaluate how post stent dilatation with large balloons has impact on stent elongation. Methods: Four kind of stents (Fig1-b) were deployed into a silicon tube model; 10mm of one side of the stent was attached to the model wall and 10mm on the opposite side of the stent was free from the vessel wall (Fig1-a). Then, in each model, post stent dilatation (PD) (Fig1-b) was performed with four different kind of 3.5mm balloons at nominal (NP) and rated balloon pressure (RP). A total of 16 stents were tested, and difference of degree of stent elongation in the stent portion which was free from the wall (delta stent length) was measured and compared among different kind of stents and different kind of balloons. Furthermore, four kind of deployed stents were also dilated three times at RP to evaluate the impact of repeated dilataton on stent elongation. Result: Stent elongation was observed in all models. Delta stent length before and after PD at NP and RP were 0.41±0.15mm and 1.15±0.37mm, respectively. Compared with different four kind of stents, there was no significant difference in delta stent length before and after PD at both NP and RP (p=0.58, 0.96, respectively), however compared with different four kind of post dilatation balloons, significant difference in delta stent length before and after PD was observed at both NP and RP (p=0.016, <0.001, respectively). Moreover, repeated post dilatation led to delta stent length was getting longer in all stents, and the degree may also depends on difference kind of stents. ![Figure][1] Conclusion: Stent elongation after post stent dilatation was observed in this ex vivo model which may be mainly influenced by the type of post dilatation balloons and dilatation pressure. Repeated post dilatation may have an effect on aggravation of stent elongation. [1]: pending:yes