The present work attempts to investigate the influence of hygrothermal environments on the buckling of soft-core sandwich plates with laminated composite face sheets. The stability equations are derived based on piecewise low-order shear deformation theory (PLSDT) and then solved using different methods, depending on the boundary conditions. For fully simply supported sandwich plates, an analytical method is developed which results in some closed-form solutions. For sandwich plates with two parallel simply supported edges and two clamped edges, a semi-analytical solution is established using one-dimensional generalized differential quadrature (GDQ) technique. Finally, for fully clamped sandwich plates, twodimensional GDQ approach is applied to the governing equations. To validate the results of proposed methods, a comparative study with various examples is carried out verifying that the methods in the present work can accurately predict the buckling load of sandwich plates in hot and wet environments. Then, a comprehensive parametric study is performed to show the effects of temperature and moisture content on the buckling of sandwich plates for different parameters such as length-to-thickness ratio, core thickness, and boundary conditions. It is concluded that both temperature and moisture content have significant influences on the buckling behavior of sandwich plates.