The epoxy composites filled with 5 and 10 mass % of sodium bicarbonate were prepared. Sodium bicarbonate at the heating decomposes into sodium carbonate, carbon dioxide and water. As a result, sodium bicarbonate is able to slow down the combustion process when it used as polymer filler. The thermal stability of the prepared samples was investigated at the heating in air using thermal analysis. The mechanical characteristics of epoxy composites were also studied. The gaseous products of thermal oxidative degradation were studied using mass spectrometric analysis. It was found that sodium bicarbonate accelerates the process of thermal oxidative degradation of the epoxy composites in the initial stage, but enhances thermal stability in the final stage. The addition of boric acid to sodium bicarbonate as filler is recommended to improve the thermal stability of the epoxy polymer.