The influence of temperature and moisture on the hygrothermal behavior of laminated composite plates resting on elastic foundations is investigated using a refined plate theory. The material properties of the composite are affected by the variation of temperature and moisture. The present plate theory enables the trial and testing of different through-the-thickness transverse shear-deformation distributions and, among them, strain distributions that do not involve the undesirable implications of the transverse shear correction factors. The governing equations are derived based on the present theory, including hygrothermal effects and elastic foundation parameters. The effects of Winkler and Pasternak foundation parameters, temperature, moisture concentration, transverse shear deformation, plate aspect ratio, side-to-thickness ratio on deflections and stresses are investigated.