Three kinds of mesoporous silica (MCM-41, FSM-16 and SBA-15) of different pore size and texture were synthesized by templating method. Co-B nanoparticle catalysts were supported over these mesoporous silica by impregnation–reduction method in order to study the effect of support pore structure on the catalytic properties in H2 production by hydrolysis of Ammonia Borane (AB). TEM and N2 adsorption–desorption isotherm results clearly revealed that size, dispersion degree, and location of Co-B particle is affected by the pore texturing of the support. It also showed that the catalyst particle acquires directly the size of the support pores only for SBA-15 whereas there is no correlation of the particle size and pore size for MCM-41 and FSM-16. Co-B supported over SBA-15 silica was found to be the most active catalyst as inferred from the observed hydrogen generation rates in the hydrolysis reaction compared to that produced by MCM-41 and FSM-16 supported catalyst. Higher activity for SBA-15 support is mainly attributed to the geometrical confinement of Co-B particles within the pores which creates smaller Co-B particles (6 nm) with uniform size distribution and higher degree of dispersion as compared to MCM-41 and FSM-16 support where the Co-B particles lie on the external surface with broad size distribution. Open and interconnected pores of SBA-15 can also provide easy passage for reactant and product during the course of reaction. The Co-B particles supported in the interconnected pores of SBA-15 produce lower effective activation energy barrier related to the hydrolysis process of AB than that established with MCM-41 and FSM-16 supported catalyst. Most importantly, the thicker pore walls of SBA-15 assist in avoiding the agglomeration of Co-B particles and even provide high stability at elevated temperatures (873 K) at which unsupported Co-B catalyst gets completely destroyed.