Large scale buckling test under vacuum pressure was carried out to check the buckling strength of the tank. The test tank was the inner tank of the existing LPG above ground tank. The test was performed using depressurization method by evacuating the water contained in the inner tank. In the test, the first buckling response occurred at the pressure of 1.72kPa and the buckling deformation in less than 90% area of circumferential direction occurred at the pressure of 2.21kPa. Buckling was also confirmed to be an elastic buckling. The reduction factor against the calculated value of buckling pressure was 0.7, which was almost the same as the value already obtained for a small and middle size test specimens. Then, many important information on buckling was obtained.