With 0.1-1.5％ polyaluminophenylsiloxane as catalyst，the rate of curing of poly-methylphenylsiloxane resin increases．The apparent energy of activation of curing falls from 26 kcal／mole in the absence of the catalyst to 20 kcal/mole in its presence，being little affected by the amount of catalyst used．However，the apparent frequency factor of curing increases with the increase of the catalyst，being one order of magnitude higher with 0．6％catalyst than without．There are two stages in the thermal oxidative degradation of the thermally cured polymethylphenylsiloxane resin．The methyl groups decompose at a much lower tem-perature than the phenyl groups．The addition of the polyaluminophenylsiloxane during the curing of the resin raises the initial temperature of decomposition of the methyl group and lowers that of the phenyl group．With increasing amount of the catalyst used，the difference in the temperature of decomposition gradually diminishes．