It is proposed that the technique to generate planar elongational flow with high elongational rate by using core/sheath flow. In this study we carried out experiments to observe flow behavior for both viscous fluid and viscoelastic fluid in the flow. In case of viscous, we compared experimental results of velocity distribution along a centerline of the flow cell to analysis results under the two-dimensional Poiseuille flow and they show good agreement. On the other hand, it is observed for viscoelastic fluid that flow behavior of the core fluid shows four kind of flow patterns from result of flow visualization and velocity profile, that is, swelling, stretching, stretching before conjunction region and instable flow. Next, we evaluated molecular orientation profile of elongated fluid by using crossed nicols method. As the results, measure of molecular orientation doesn't depend on the distance to sidewalls of the flow cell in elongational flow region. It is shown that contribution elongational property to the flow can be discuss from results of distribution of molecular orientation along center line of the flow cell.