One of the authors presented the theoretical study on the behavior of the detached bottom plate from the foundation due to welding deformation under liquid pressure in the first report. In this report, the results of experimental model tests using polycarbonate plate are presented. As the pressure increases gradually, the deformed plate begines to touch to the foundation from both sides of the detached part, and at a critical pressure, the whole plate touches to foundation completely in an unstable manner as predicted by the theory. The relationships between pressure and deflection as well as the critical pressure agree well with theoretical predictions. Consequently, it is concluded that the theory is useful for prediction of the behavior of the actual tank bottom plate under liquid pressure in practical accuracy. The occurence of plastic hinge in the plate in case of large welding deformation and the redetaching load in the process of unloading are also discussed.