Polyelectrolyte hydrogels containing diprotic acid moieties sensitive to ionic strength changes of the swelling medium were synthesized from N,N-diethylaminoethyl methacrylate (DEAEMA), N-vinyl-2-pyrrolidone (VP) and itaconic acid (IA) by using ammonium persulfate (APS) as a free radical initiator in the presence of the cross-linker, methylenebisacrylamide (MBAAm). The swelling behavior of the ionic poly [(NN-diethylaminoethyl methacrylate)-co-(N-vinyl-2-pyrrolidone)] [P(DEAEMA/VP)] hydrogels were investigated in pure water; in NaCl solutions with pH 4 and 9; and in water-acetone mixtures depending on the IA content in the hydrogel. The average molecular mass between cross-links (M-c) and polymer-solvent interaction parameter (chi) of the hydrogels were determined from equilibrium swelling values. The pulsatile swelling behavior was also observed in response to solvent changes between the solution in water and in acetone. The equilibrium swelling ratio of these hydrogels was basically unaffected with change in temperature. The swelling variations were explained according to the swelling theory based on the hydrogel chemical structure.