Mixed monolayers composed of fatty acid and polyamic acid containing azobenzene on a water surface were investigated by means of the Maxwell displacement current(MDC) measurement method. The MDCs were generated across mixed monolayers due to the compression of fatty acid and polyamic acid. The surface pressure and MDCs generated were also investigated in connection with monolayer compression and expansion cycles. It was found that MDCs were generated over the entire range of molecular area, and the maximum of MDCs appeared at the molecular area just before the initial rise of surface pressure in compression.