In this paper fluid-structure interaction of vibrating composite piezoelectric plates is investigated. Since the plate is assumed to be moderately thick, rotary inertia effects and transverse shear deformation effects are considered by using exponential shear deformation theory. Fluid velocity potential is obtained using the Laplace equation and fluid boundary conditions and wet dynamic modal functions of the plate are expanded in terms of finite Fourier series to satisfy compatibility along the interface between plate and fluid. The electric potential is assumed to have a cosine distribution along the thickness of the plate in order to satisfy the Maxwell equation. After deriving the governing equations using Hamilton’s principle, the natural frequencies of the fluid-structure system with simply supported boundary condition are calculated using the Galerkin method. The model is compared with the available results in the literature and then the effects of different variables such as depth of fluid, the width of fluid, plate thickness and aspect ratio on natural frequencies and mode shapes are illustrated.