Buckling failures are often observed for tanks subjected to seismic load. In this paper, the dynamic buckling is studied, using small plastic cyrindrical tanks made of a polyester sheet. The static buckling tests of the fluid filled tanks subjected to lateral load, and the dynamic buckling tests under harmonic excitation by a shaking table are carried out, and the buckling modes are compared. The stress resulting from the frequency response (the circumferential wave numbers n=1 for horizontal excitation and n=0 for vertical excitation) is calculated using an axisymmetric shell finite element program including the effect of fluid structure interaction and static buckling stress criteria are applied to the above calculations in order to predict the appearance of buckling. The predictions are compared with test results and prove to be fairly satisfactory in the restricted region under the natural frequency of the fundamental mode.