The kinetics of the catalytic decomposition of dichloromethane and trichloromethane in a single row plug flow reactor at 400–500°C has been studied. Dichloromethane decomposes into carbon and hydrogen chloride (presumably via the intermediate formation of monochlorocarbene). Trichloromethane decomposes mainly into carbon, hydrogen chloride and tetrachloromethane (presumably via the intermediate formation of dichlorocarbene).