A styrene-N,N-dimethyl(maleamidic acid)propyl ammonium propane sulfonate (SDMMAAPS) copolymer was synthesized through an amicloacidation reaction of a styrene-maleic anhydride alternating copolymer with N,N-dimethylaminopropylamine (ring-opening reaction) and then reacted with propane sultone. The cloud point and minimum salt concentration (msc) of this ampholytic SDMMAAPS copolymer were determined in aqueous salt solutions. The effects of counterions on the cloud point and msc of SDMMAAPS were not entirely the same as those of other zwitterionic poly(sulfobetaine)s. The greatest difference from other poly(sulfobetaine)s, such as styrene-N,N-dimethyl(maleimido propyl)ammonium propane sulfonate copolymers, was the carboxylic group on the polymer chain unit of SDMMAAPS. (C) 2003 Wiley Periodicals, Inc.