In the present study, a theoretical method is developed to investigate free vibrations of circular plates immersed in fluids and a series of experimental tests are presented to validate the model. The coupled governing equations of both hydroelastic vibration of the plate and liquid sloshing are solved by a semi-analytical procedure, simultaneously. The effect of the plate, used as a baffle, on suppression free surface waves is also considered. Plates with two different boundary conditions, free-edge and clamped edge, are studied. The fluid domain is non-convex because of the presence of the plate, which introduces a singularity in the formulation of the fluid velocity potential. Both the least square and Galerkin methods are applied to determine the unknown coefficients in the velocity potential. Natural frequencies and mode shapes are obtained using the Rayleigh-Ritz method, taking fluid-structure interaction into account. The present approach is validated by comparison to results of modal test on two different steel plates with the free edge and submerged in water, as well as comparison to those of a commercial finite element code. The results obtained from the present method agree with those obtained from modal test and the finite element analysis.