Magnesium hydroxide eliminates DSC exotherm of polypropylene oxidation and thus the peroxidation process. At the same time, non -isothermal thermogravimetry experiments show that the temperature o f the maximum rate of volatiles released due to polypropylene decomposition is significantly higher than that from original polypropylene. It appears that in the presence of magnesium hydroxide, the degradation products are not formed predominantly from decomposition of peroxides but from direct scissions of polypropylene chains. Chemiluminescence experiments confirmed that magnesium ions in alkaline conditions have the activating effect on oxygen from surroundings contributing thus to the more pronounced oxidation of soot and to the decrease of the smoke released during polypropylene burning. The links with the burning of the polypropylene with alkaline magnesium compounds were searched .