The properties of ampholytic poly[N,N’ - dimethyl(acrylamido propyl) ammonium propane sulfonate] (poly(DMAAPS)) in aqueous solution were studied by measurements of cloud point determination and intrinsic viscosity. The minimum salt concentration and intrinsic viscosity of this polyampholyte were related to the type and concentration of added salt. ’Soft’ salt cations and anions bound more easily to the quaternary ammonium (R(4)N(+)) and sulfonate groups (SO3-) of poly(DMAAPS) than ’hard’ salt cations and anions. For the measurements of cloud point and intrinsic viscosity in aqueous salt solution of various divalent acidic groups, the divalent acidic groups ruptured the ionically crosslinked network of sulfobetaine at a small concentration of salt and the divalent acidic groups attracted the neighbouring polymeric side chains to make the polymeric main chains twist and agglomerate. A similar degree of expansion of the polymeric main chain at the saturated binding concentration of various monovalent salts (LiCl, NaCl, KCl) was observed from measurement of intrinsic viscosity.