The copolymer prepared by copolymerizing acrylamide with maleic anhydride was imidized with N,N-dimethylaminopropylamine. The obtained acrylamide-N,N-dimethylaminopropylmaleimide (ADAPM) copolymer was then reacted with propane sultone to yield a novel acrylamide-N,N-dimethylmaleimidopropylammonium propanesulfonate (ADMMAPS) copolymer. The properties of this ampholytic ADMMAPS copolymer in aqueous salt solution were studied by measurement of reduced viscosity and intrinsic viscosity. The intrinsic viscosities of this polyampholyte were related to the type and concentration of the added salts. ’Soft’ salt cations and anions were more easily bound to the quaternary ammonium (R(4)N(+)) and sulfonate group (SO3-) of ADMMAPS than were ’hard’ salt cations and anions. The tendency of the intrinsic viscosity for ADMMAPS in various aqueous salt solutions is similar to that of other zwitterionic poly(sulfobetaine)s. The Huggins constant for ADMMAPS in an aqueous salt solution shows a marked distinction from the sulfobetaine copolymer, styrene-N,N-dimethylmaleimidopropylammonium propane sulfonate (SDMMAPS). This phenomenon is attributed mainly to the presence of the acrylamide/styrene segment, a hydrophilic/hydrophobic group, on the ADMMAPS/SDMMAPS copolymer, respectively.