An air gap membrane distillation system having a polytetrafluoroethylene (PTFE) hydrophobic porous membrane was used for the removal of water from nitric acid/water mixtures. The influences of the feed temper- ature, feed concentration, flow rate, and air gap on the permeate flux and the selectivity of water were studied. The selectivity of water and flux were decreased with increasing feed concentration. With increasing feed flow rate and feed temperature, a decrement in the selectivity of water and an increment in flux were observed. The effect of the air gap thickness was also examined. Recirculation significantly changed the flux and nitric acid concentration in the permeate. This process share the best performance for the removal of water as vapor from nitric acid mixtures through a hydrophobic porous membrane.