Abstract: Disclosed herein is a process for preparing with a high yield an aminoalkylsulfonic acid represented by the following general formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are each a hydrogen atom, an alkyl group having 1-3 carbon atoms or a hydroxyl-containing alkyl group having 1-3 carbon atoms and n stands for an integer of 2 or 3, which process comprises reacting a sulfite with a halogenated alkylamine represented by the following general formula: ##STR2## wherein X means a chlorine, bromine or iodine atom, and R.sub.1, R.sub.2, R.sub.3 and n have the same meanings as defined above by adding the halogenated alkylamine little by little either continuously or intermittently over a certain period of time to a heated aqueous solution of the sulfite.