This paper discusses the dehydrogenation of ammonia borane (AB) and MCM-41/AB nanocomposites in which the loading level of AB (i.e., the mass ratio of AB to mesoporous silica) varies from 0.11 to 2.36. The dehydrogenation temperatures shift to low temperatures with decreasing loading levels. At loading levels of 0.11 and 0.15, only one dehydrogenation step is observed at temperatures less than 200 degrees C. Our results also show that 12.6 wt % of hydrogen in the incorporated AB is liberated from the nanocomposite at a loading level of 0.15 in 1 h at 89.5 degrees C. We deduce that AB confined within the mesopores is amorphous, while AB outside of the channels has a tetragonal structure. Furthermore, we deduce that at relative low loading levels AB coats the inner surface of mesoporous silica as a monolayer.