PURPOSE: To lower a dioxane content by reacting a specific amt. mixture of two compds. expressed by specific general formulas with a specific. amt. of chlorosulfonic acid at 20 to 120°C and neutralizing the product thereof in a specific metal hydroxide.

CONSTITUTION: The mixture composed of 99 to 5 mol.% compd. expressed by formula I (R denotes an 8-18c alkyl group or the like) and 1 to 95 mol.% compd. expressed by formula II (R' denotes an 8-17C alkyl group; (b) denotes an integer from 1 to 20; (c) denotes 0, an integer from 1 to 20) is prepd. This mixture is in a liquid form and is reacted with 0.95 to 1 mol.% chlorosulfonic acid or SO3 per mol of the -CH2CH2OH- group included in the mixture. The product is then neutralized by an aq. soln. of a compd. expressed by formula III (R2 to R5 denote each a 1-4C alkyl group or the like), by which the surfactant mixture is obtd.