Cl-free Ru/CeO2 spherical catalysts were prepared by incipient wetness impregnation and subsequent washing processes using RuCl3 center dot 3H(2)O and a commercial spherical CeO2 support. Cs addition improved the catalytic performance for NH3 decomposition, and the optimal Cs loading was a Cs/Ru molar ratio of 0.43. Transmission electron microscopy (TEM) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) suggested that Cs was present around Ru metal particles and served as an anchor for forming small, well-dispersed Ru metal particles (similar to 2 nm). CO2 temperature-programmed desorption results indicated that the Cs-Ru/CeO2 catalyst had more strong basic sites than the Ru/CeO2 catalyst. Kinetic analysis results clearly demonstrated that Cs addition promoted recombinative desorption of N atoms, which is the rate-determining step of NH3 decomposition. Consequently, the Cs-Ru/CeO2 spherical catalyst (Cs/Ru = 0.43) treated in Ar for 1 h at 773 K exhibited high catalytic activity for NH3 decomposition (NH3 conversion: 40% at 523 K and 80% at 573 K) at 2000 mL-NH3 g cat(-1) h(-1).