Thermoanalytical (thermogravimetry, differential thermogravimetry, and differential thermal analysis) and structural (IR spectroscopy, light microscopy, etc.) methods were employed to estimate the thermal behavior of binary blends of poly(ethylene oxide) (PEO) with copper(II) bromide (CuBr2) of various concentrations under the conditions of a broad temperature interval. Solid residues obtained after heating the blends at different characteristic stages of the thermal destruction were also studied. CuBr2 introduced in concentrations of 5-10% exhibited a significant thermostabilizing effect on PEO in an air medium, regardless of the mode of the blend preparation. No data about the formation of crystallizing complexes or new compounds prepared from the starting materials on heating the blends were obtained within the concentration range studied (0.1-40% CuBr2). An assumption for the formation of associations between the oxygen atoms of PEO and the metal ion, which obstruct the thermal oxidation processes to a certain degree, were made in order to explain the antioxidative mechanism of action of the inorganic salt.