A semi-interpenetrating polymer network (semi-IPN) hydrogel composed of chitosan and polyacrylonitrile (PAN) exhibited electrical-sensitive behavior. The swelling behavior of the semi-IPN was studied by immersion of the gels in aqueous NaCl solutions at various concentrations. The swelling ratio decreased with an increase in the concentration of the electrolyte solution. The stimulus response of the semi-IPN hydrogel in electric fields was also investigated. When swollen, the semi-IPN was placed between a pair of electrodes, and it exhibited bending behavior upon application of an electric field. The electro responsive behavior of the semi-IPN was also affected by the electrolyte concentration of the external solution. The semi-IPN also showed various degrees of increase in bending behavior depending on the electrical stimulus. (C) 2003 Wiley Periodicals, Inc.