We investigated the effect of charge densities of the gel network and ionic strength of solution on swelling behaviors of ionized gels. We used the modified double-lattice model, Flory-Erman's elastic model, and the ideal Donnan theory to describe swelling behaviors of the electrolyte bounded hydrogels. Energy parameters (epsilon/k, deltaepsilon/k) were obtained from fitting liquid-liquid equilibria data of the linear poly-N-isopropylacrylamide/water system and two adjustable model parameters obtained from a nonelectrolyte hydrogel system. Calculated values agreed with experimental data for the given systems.