This paper examines the vibrational characteristic of a horizontal functionally graded (FG) rectangular plate submerged in fluid medium. Young's moduli and mass density vary continuously in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents, while other properties are assumed to be constant. The fluid is considered to be ideal, incompressible, inviscid and irrotational, thus the effects of hydrostatic pressure and free surface waves are not taken into account. Governing equation for the fluid-plate system is derived based on the first-order shear deformation theory. The fluid velocity potential is derived from the boundary conditions for the plate-fluid system and is used to determine the added mass. To demonstrate the accuracy of the present analytical solution, a comparison is made with those reported in open literature. The influence of different parameters including interaction boundary conditions, power law index, metal-to-ceramic Young's modulus, density ratios of the FG plate, thickness to length ratios, aspect ratios, fluid density and fluid depth on the nondimensional natural frequencies of FG rectangular plate are quantitatively examined and discussed in tabular and graphical forms.