Poly(L-lysine) (PLL) undergoes structural change from alpha-helix to random coil in response to a change in pH in an aqueous solution. By chemical crosslinking of PLL with ethylene glycol diglycidyl ether (EGDE), we prepared pH-responsive hydrogels that undergo a change in volume and conformation between a-helix and random coil in response to a change in pH. The difference in transition pH between a PLL linear polymer and a PLL hydrogel revealed that chemical crosslinking stabilized the helical structure of PLL chains in hydrogel networks.