A wavelet analytic technique has been developed for the non-stationary seismic response of fixedbase liquid storage tanks. The ground acceleration has been characterized through estimates of statistical functionals of wavelet coefficients generated from a single accelerogram of a ground motion process. The tank-liquid system has been modeled as a two-degree-of-freedom (2-DOF) system. Both sloshing and impulsive actions of the tank liquid are considered. The wavelet domain dynamic equations have been formulated and solved to find out the coefficients of hydrodynamic pressure on the tank wall, base shear, and overturning moment at the tank base. Closed form expression for the instantaneous power spectral density function (PSDF) of the response quantities in terms of the functionals of the input wavelet coefficients has been obtained. The moments of this PSDF are used to estimate the expected largest peak coefficients of the hydrodynamic pressure, base shear and base moment developed in the tank. Parametric variations are carried out to study the effects of the height of liquid in tank and the ratio of liquid height to tank radius on the tank responses.