Free transverse vibration of a circular plate with thickness varying as (1 + α x + x 2 ) has been studied when the edge of the plate is clamped or simply-supported. The Rayleigh-Ritz method with suitable choice of basis functions satisfying the essential boundry conditions, has been employed to find the fundamental frequency and the associated mode shapes for various values of α and β with different boundary conditions. The convergence of results is ensured by working out several approximations till the results converge to the desired accuracy. The results for uniform thickness, linear and parabolic variation of thickness have been obtained as special cases. Tables and graphs are given for frequency, mode shapes and for depicting the effect of parameters α and β on the frequency.