Gold-nickel nanoparticles (NPs) of 3-4 nm diameter embedded in silica nanospheres of around 15 nm have been prepared by using [Au(en)(2)Cl(3)] and [Ni(NH(3))(6)Cl(2)] as precursors in a NP-5/cyclohexane reversed-micelle system, and by in situ reduction in an aqueous solution of NaBH(4)/NH(3)BH(3). Compared with monometallic Au@SiO(2) and Ni@SiO(2), the as-synthesized Au-Ni@SiO(2) catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen. During the generation of H(2), the synergy effect between gold and nickel is apparent: The nickel species stabilizes the gold NPs and the existence of gold helps to improve the catalytic activity and durability of the nickel NPs.