Discharge of granular materials through a standpipe against an imposed overall gas pressure difference has been studied experimentally. The particles were transported from a low pressure region to a high pressure region and discharged through an orifice by aeration. With air introduced to aerate the particles, particle flow against the pressure difference was found to be more stable than without aeration. The particles can be discharged through the orifice stably even when the overall pressure difference in the pipe is just below that for fluidization. The mass flow rate of particles is correlated to the pressure difference across the discharging orifice and to its diameter. Effects of aeration on discharging rate were examined. An experimental equation which correlates the particle flow rate to the pressure difference across the orifice was obtained.