The thermodynamic properties of the ABO3 perovskite-type compounds are strongly affected by the A- and B- site substitution and the oxygen nonstoichiometry. The paper presents the thermodynamic properties of some doped nano- and microstructured lanthanum manganites of general formula La1-xMxMn1-yMeyO3 (where M=Sr, Ca; Me=Al; x=0.3;0.33, y=0;0.05) which have been studied within the temperature range of 873-1273 K in a reducing atmosphere (10-6 Pa). The relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase and the equilibrium partial pressures of oxygen have been obtained by using a solid electrolyte galvanic cell method. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with measurements of the electromotive force (EMF). The focus of the research was to emphasise modifications of the thermodynamic properties connected with the nanocrystalline state. The results obtained are discussed in relation to significant changes in the overall concentration of defects.