The desorption of ammonia from a dilute aqueous solution, its transport through a hydrophobic porous membrane and absorption by a sulfuric acid solution on the other side of membrane were remarkably accelerated by making use of the temperature difference between the feed and stripping solutions. Ammonia transfer was accompanied by pervaporation of water. Equations describing concurrent unsteady-state mass transfer of ammonia and water were derived, and they coincided well with the experimental results.