Experiments have been carried out to study the effect of air injection on the wall pressures in the near field of deflectors placed in a duct. Various quantities of air have been injected just downstream of the ramps to form stationary air cavities. The variation of the cavity length has been studied as a function of the ratio of the volume of airflow to the water discharge. The wall pressure field in terms of the mean and fluctuating parts is presented. This study shows how air injection affects the wall pressure field from that without air injection. Information concerning wall pressures is expected to be useful in the design of deflectors in tunnels and spillways.