Maxwell displacement current(MDC) measuring technique has been applied on the study of monolayers of polyamic acid containing p-cyanoazobenzene. The displacement current was generated from monolayers on the water surface by monolayer compression and expansion. Displacement current was generated when the area per molecule was about $140{AA}^2$ and $100{AA}^2$. Maxwell displacement currents were investigated in connection with monolayer compression cycles. It was found that the maximum of MDC appeared at the molecular area just before the initial rise of surface pressure in compression cycles.