Superbase zinc soaps in the form of zinc carboxylates, in which the carboxylic acids consisting of a mixture or otherwise of satured organic carboxylic acids containing from 7 to 13 carbon atoms, having the following characteristics: a linear acid content of between 0 and 40 % by weight, a content of acids which are branched on carbon 2 of between 0 and 20 % by weight, and a content of acids which are mono- or polysubstituted on carbon 3 and/or on the carbons of higher rank, which is equal to or greater than 50 % by weight; their preparation and use as polymer stabilisers particularly for polyvinyl chloride.