Dialkyl sulphosuccinates containing less than 0.3% maleate/fumarate may readily be prepared at high concentrations (77-90% by weight) by the sulphitation of the corresponding dialkyl maleates/fumarates in a mixture of C 1 -C 4 alcohol and water, without the need for other solvents or special catalysts, because at this very high concentration level there exist coinciding regions of low viscosity at both reaction and storage temperatures. The sulphiting agent is used in solid form, and inorganic solids are removed by filtration or other physical separation methods at the end of the reaction.