Ammonium fatty acid hydroxyalkanesulfonates are made by a process in which (a) ammonium hydroxyalkanesulfonate corresponding to general formula (I):HO--(C.sub.n H.sub.2n)--SO.sub.3 NH.sub.4 (I)wherein n=2 to 4, is subjected to the esterification reaction with a fatty acid corresponding to the formula (II)R--COOH (II)wherein RCO is an aliphatic, linear or branched acyl radical containing 6 to 18 carbon atoms, in the presence of an esterification catalyst, characterized in that (a) before the esterification reaction, the starting compounds corresponding to formulae (I) and (II) are dried at a temperature of 120.degree. C. to 160.degree. C. and under a pressure of 100 to 700 mbar; (b) the esterification reaction is carried out at a temperature above 160.degree. C. to 195.degree. C. and under a pressure of 250 mbar to atmospheric pressure; (c) water of solution and water of reaction formed are directly removed from the reaction mixture; (d) the catalyst is neutralized with a base on completion of the reaction.