Thermal dehydrogenation of ammonia borane (AB) is one of the simplest methods to generate pure hydrogen for hydrogen power-driven proton exchange membrane fuel cells. For AB thermolysis, it is imperative to develop a highly effective catalyst to initiate the dehydrogenation reaction at a low temperature and eventually achieve enhanced hydrogen production. Here, we introduce a specifically designed AB-SiO2 nanocomposite, which is prepared by simple mixing and pressing processes. Hydrogen evolution during thermolysis of the cotton-structured AB-SiO2 composite is initiated at around 80 °C, and the maximum H2 yield is determined to be 11.2 wt% (2.32 mole equivalents of H2). The yield is found to depend on the size and size distribution of the catalytic SiO2 particles in the hydrogen fuel composite.