In this study, we investigated control of particle size of hollow silica-alumina composite spheres prepared using L(+)-arginine and their activity of these hollow spheres for hydrolytic dehydrogenation of ammonia borane. The hollow spheres were prepared by polystyrene templates method, and the polystyrene templates were completely removed by calcination. In this method, silica-alumina composite shell were coated onto polystyrene particles via a sol-gel reaction using L(+)-arginine as a promoter of this reaction. Hollow spheres with average diameter of 206, 277, and 366 nm were prepared using polystyrene particles with average diameter of 150, 200, and 340 nm, respectively. Activities of hollow spheres with various diameter for hydrolytic dehydrogenation of ammonia borane were compared. The evolution of 8, 7.5, and 5 mL of hydrogen was released in the presence of the hollow spheres with the diameter of 210, 260, and 400 nm, respectively. From the results, the activity increase with decrease of diameter of the hollow spheres. The result of neutralization titration and solid state ²⁷Al MAS NMR indicates that the activity for hydrolytic dehydrogenation of ammonia borane increase with increase of amount of Brønsted acid sites.