A composition for binding environmentally-harmful substances in solid or semi-liquid state contains caustic magnesium oxide, non-ferrous metal salts as a hardener, non-ferrous metal oxides catalyzing formation of radial crystalline structures, and optionally water and other additives. A method of stabilization of environmentally-harmful substances binds these substances in the solid state or semi-liquid state in the composition containing caustic magnesium oxide, wherein the environmentally-harmful substances are supplemented by the composition containing caustic magnesium oxide, non-ferrous metal salts as hardener, non-ferrous metal oxides catalyzing formation of radial crystalline structures, and optionally water and other additives. A form of paste is obtained, followed by leaving the mixture for solidification and stabilization of the product. Use of non-ferrous metal salts in connection with non-ferrous metal oxides catalyzing formation of radial crystalline structures stabilizes the environmentally-harmful substance with the use of caustic magnesium oxide.