Abstract: The invention relates to a method for isolating concentrated paraffin sulfonic acids from reaction mixtures that are produced during the sulfoxidation of n-paraffins, from which a major part of the sulfuric acid and the paraffin was removed by phase separation and which contain, in addition to the free paraffin sulfonic acids, n-paraffins, water and optionally minor amounts of sulfuric acids. The method according to the invention is characterized by removing paraffin and optionally residual water by vacuum distillation. The paraffin sulfonic acids obtained by distillation have a content of more than 85% by weight of the active substance. The material is pale, odorless and low in sulfuric acid and paraffin.