Abstract: There is provided by the present invention a twopart room temperature vulcanizable silicon rubber composition which is exceptionally stable to reversion and specifically to reversion of the cured composition caused by water comprising a silanol-stopped diorganopolysiloxane, filler, an alkyl silicate and a catalyst where the catalyst is a reaction product of an organic tin oxide compound with the hydrocarbon ester of an oxygen-containing acid having at least one oxygen atom in the acid radical attached to a replaceable acid hydrogen atom. The hydrocarbon ester can be either an inorganic acid or a carboxylic acid. The preferred catalyst in the present invention is the reaction product of dibutyl tin oxide and a phthalate ester.