We report on the synthesis, physicochemical characterization and catalytic evaluation of the acid-base properties of mesoporous MCM-41 aluminosilica oxynitride materials. The materials were prepared by subjecting Al-grafted aluminosilicate MCM-41 materials with varying Al content to nitridation, i.e., treatment with ammonia at high temperature. The mesoporous aluminosilica oxynitride materials were well ordered and possessed high surface area and pore volume. The nitrogen content of the oxynitride materials varied from 5.4 to 15.7-wt% depending on the Al content of the parent MCM-41. Nitrogen was incorporated into aluminosilicate framework to generate various NHx species, including terminal NH2 and bridging NH groups as well as adsorbed ammonium ions. The relative amount of terminal NH2 and bridging NH groups depended on the Al content. The oxynitride materials were found to exhibit both acidic and basic surface functionality.