Abstract: A method of producing a bis(2-carboxyethyl)-alkyl phosphine oxide represented by the following general formula (1) is disclosed. ##STR1## The method comprises the following Steps 1-4: step 1 wherein phosphine is reacted with acrylonitrile to produce bis(2-cyanoethyl)phosphine and then, in step 2, reacted with an alkene to produce a bis(2-cyanoethyl)alkyl phosphine, and in step 3, reacted with an oxidizing agent to produce a bis(2-cyanoethyl)alkyl phosphine oxide, and in step 4, said bis(2-cyanoethyl)alkyl phosphine oxide is reacted with water or a lower alcohol to give a bis(2-carboxyethyl)alkyl phosphine oxide or a derivative thereof.