In this paper, classical plate theory is used to analyse free oscillation of rectangular plates made of porous FGM material, edge joints on Winkler elastic base. Three different types of pore distribution: uniform distribution, symmetric irregular distribution and asymmetrical irregular distribution are investigated. The reliability of the analytical solution as well as the calculation program written on Matlab are verified with some published results and with the results calculated by the SAP2000 structural calculation software. The influence of the material parameters, the geometrical dimensions of the plate, as well as the background coefficient on the free oscillation frequency of the plate are evaluated.