Three ceria nanocrystals with different morphologies (nanocubes, nanorods, and nanoparticles) were synthesized and used as supports to evaluate the support morphology-dependent ammonia synthesis activity in the structure-sensitive ammonia synthesis reaction. The Ru/r-CeO₂ catalyst shows a higher catalytic reaction rate (3830 μmol g⁻¹ h) than that of Ru/c-CeO₂ (1289 μmol g⁻¹ h) and Ru/p-CeO₂ (529 μmol g⁻¹ h) under the reaction conditions of 400 °C, 1 MPa, and 60 mL min⁻¹. In addition, promoters (Cs, K, and Ba) can effectively enhance the catalytic activity of the catalysts such as 2Cs–Ru/r-CeO₂ (14266 μmol g⁻¹ h) and 2K–Ru/r-CeO₂ (11227 μmol g⁻¹ h). The effect of the morphology of the CeO₂ support on the metal–support interaction and catalytic performance of the Ru/CeO₂ catalysts can be correlated to the exposed crystal planes and surface composition/electronic structure of the CeO₂ support with diverse morphologies.