The influence of temperature and moisture on the bending behavior of composite functionally graded material (FGM) plates resting on elastic foundations is investigated. A transverse shear and normal deformation theory are used with five unknown functions as opposed to six or even greater numbers in the case of other shear and normal deformation theories. An accurate solution is presented in the hygrothermal response of the FG plate with simply-supported edges and resting on elastic foundations. The interaction between the plate and the elastic foundations is considered and included in the equilibrium equations. The influences of Winkler and Pasternak foundation parameters, temperature, moisture concentration, thickness stretching, shear deformation, plate aspect ratio, sideto-thickness ratio, and volume fraction distribution on the plate bending characteristics are studied in detail. Numerical results for the hygro-thermo-mechanical response of the FG rectangular plates is investigated and some of them are compared with those available in the literature.