The solid-oxide electrolyte galvanic cell method has been employed in order to obtain thermodynamic properties of the brownmillerite-like compounds SrFeO2.5 and SrMnO2.5 within the temperature range of 1073-1273 K. The standard Gibbs energy, the enthalpy and the entropy of formation, as well as the partial pressures of oxygen have been obtained. The experimental thermodynamic data have been compared to the existing theoretical estimated values.