Development of low-cost and high-performance catalysts for hydrogen generation via hydrolysis of ammonia borane (NH₃BH₃, AB) is a highly desirable pathway for future hydrogen utilization. In this work, Ni nanocatalysts doped with CeO_x and supported on graphene (Ni-CeO_x/graphene) were synthesized via a facile chemical reduction route and applied as robust catalysts for the hydrolysis of AB in aqueous solution at room temperature. The as-synthesized Ni-CeO_x/graphene nanocomposites (NCs) exhibited excellent catalytic activity with a turnover frequency (TOF) as high as 68.2 min^-1, which is 49-fold higher than that for a simple Ni nanoparticle catalyst and is among the highest values reported for non-noble metal catalysts in AB hydrolysis. The development of efficient and low-cost Ni-CeO_x/graphene catalysts enhances the feasibility of using ammonia borane as a chemical hydrogen storage material, which may find application ina hydrogen fuel-cell based economy.