The copolymers of 10% acrylic acid (AAc) and 90% acryl amide (AAm) were synthesized by free radical polymerization with 5% ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The basic physical feature such as density, fixed charge density, average molecular weight, equilibrium water contentment and crosslink density were studied. In this investigation, the equilibrium and kinetic experiments were performed under three different ionic strengths, the equilibrium behavior of the hydrogels was characterized by varying the designed stimulus and by measuring the weight of hydrogel disc using a high accuracy balance. The ionic strength of the solution was adjusted with NaCl and the buffer solution was phosphoric acid. Potentiometric titration was performed to investigate the quantity of dissociated H+. Last, diffusion coefficients of aqueous sodium chloride in water swollen cross-linked poly (AAc-co-AAm) membranes were studied. A self-planned cell was used for the measurement of NaCl diffusion coefficients.