Ammonia (NH₃) decomposition to release CO_x-free hydrogen (H₂) over non-noble catalysts has gained increasing attention. In this study, three nanostructured CeO₂ with different morphologies, viz. rod (R), sphere (Sph), and spindle (Spi), were fabricated and served as supports for Ni/CeO₂ catalyst. The CeO₂ supports are different in particle sizes, specific surface area and porosity, resulting in the formation of Ni nanoparticles with distinguished sizes and dispersions. The surface properties of the Ni/CeO₂ catalysts are not only distinct but also influential, affecting the adsorption and desorption of NH₃, N₂, and/or H₂ molecules. The Ni/CeO₂-R catalyst shows superior catalytic activity compared to the other two, owing to its smaller Ni crystallite size and larger BET surface area. The most abundant strong basic sites are observed for Ni/CeO₂-Spi catalyst based on its exposed CeO₂(110) planes, which facilitates the donation of electrons to the Ni particles, benefiting the associative desorption of N atoms. Thus, Ni/CeO₂-Spi shows higher catalytic activity than Ni/CeO₂-Sph, despite their almost identical Ni crystallite sizes.