The problem of description of the formation of microporous adsorbents in a non-steady-state has been solved for the cases of thermally homogeneous and nonhomogeneous materials, A chemical model of pore formation has been proposed, The thermally homogeneous model has been applied to the treatment of some known experimental data. The theoretical results are in good correlation with the experimental results. Some recommendations about the possible further experiences which would allow testing of the proposed model have been given.