A process for producing an aminoalkylsulfonic acid of formula [2]: ##STR1## wherein R¹ and R² are each independently hydrogen, alkyl, aryl or aralkyl; and R³ and R⁴ are each independently hydrogen or alkyl, comprising reacting an aminoalkylsulfonate salt of formula [1]: ##STR2## wherein M is alkali metal, organic ammonium or ammonium ion; and R¹ to R⁴ are as described above, an aqueous solution thereof, or a solution dissolving any one of them in a water-soluble organic solvent, selected from alcohols having 1 to 3 carbon, carboxylic acids having 2 to 12 carbon and dimethylformamide, with an organic acid; and a method of salt exchange for an aminoalkylsulfonate salt of formula [1]: ##STR3## wherein M is alkali metal, organic ammonium or ammonium ion; and R¹ and R⁴ are as described above, comprising reacting the aminoalkylsulfonate salt formula [2] with a hydroxide of formula [6]:

MOH[6]

wherein M is as described above, in alcohol or water.