Abstract In the present investigation, the buckling behaviours of porous double-layered functionally graded nanoplates in hygrothermal environment are presented for the first time. The nonlocal strain gradient theory with two material scale parameters is developed to examine buckling behaviour much accurately. Based on the new first order shear deformation theory the equations of equilibrium are obtained from the principle of minimum potential energy. To simplify the equations of equilibrium and removing the bending-extension coupling, the buckling behaviours of FG nanoplates are investigated based on physical neutral surface concept. The equations of equilibrium are solved for various boundary conditions using Galerkin's method. The obtained results are compared with the results available in the literature to valid the correctness of present solution method. The effects of nonlocal parameter, strain gradient parameter, porosity volume fraction, power-law index, temperature change, humidity change and boundary conditions on critical buckling load are presented.