Existing methods of investigating the internal structure of porous materials, both experimental and theoretical, do not allow the description of micropores, To describe a microporous structure, we have proposed to relate its characteristics to the method of its production. For some kinds of microporous structures produced by random equilibrium decomposition of a primary material, we have shown the Boltzmann distribution being realized. For such structures, equations can be written for the entropy and chemical potential of micropores, using the condition of thermodynamic equilibrium between the pore and the material. A way to describe nonhomogeneous structures has been proposed, Equations have been derived for isotherms of adsorption of simple gases (without aggregation of molecules of the adsorbate). These equations are used for the treatment of experimental data, A good correlation is obtained between the theoretical and experimental isotherms. The main practical advantages of the proposed theoretical model consist in the simulation of experimental data by the theoretical curve throughout the spectrum of pressures and in the reduction of the number of semiempirical parameters employed.