Abstract: A process for preparing salts of mono-esters of sulfosuccinic acid in which maleic acid, fumaric acid or maleic anhydride, especially maleic anhydride, is reacted with a fatty alcohol, an alkoxylated fatty alcohol or a fatty acid alkanolamide; and the butenedioic acid half ester so obtained is reacted with a finely powdered crystalline sulfite of an alkali or alkaline earth metal, by mechanically mixing and butenedioic acid half ester with said sulfite in the absence of water other than that present as water of crystallization in the crystalline sulfite, to yield the desired salt of a mono-ester of sulfosuccinic acid in a solid granular form.