Abstract: By reckoning the plastic dissipation by membrane force induced by finite deflection, a modifying factor is introduced into the bending-only theory to formulate the governing equations of dynamic plastic response of rectangular plates with deflections where bending moment and membrane force are both important. Based on a kinematically admissible, time-dependent velocity field, a complete theoretical investigation is undertaken to trace the finite deflection response of simply-supported or fully-clamped rigid-plastic rectangular plates to a rectangular pulse or impulsive loading. The present prediction on the final plate deflection agrees well with the corresponding experimental results for deflections up to about 10 times of the plate thickness. This theoretical treatment improves the estimates from the bending-only theory greatly and provides a complete response (including the transient phase) analysis of the rectangular plates, the predictions are much more reliable than the previous mode approximation.