The removal of N 2 O from the atmosphere by its catalytic decomposition to N 2 and O 2 is an important process for curbing global warming. In this study, we investigated a variety of catalysts, and a ZrO 2 -supported RhO x (RhO x /ZrO 2 ) catalyst was identified as the optimum catalyst for N 2 O decomposition at a relatively low temperature (∼350 °C) in the presence of O 2 . RhO x supported on ZrO 2 performs better than RhO x loaded on other supports, as well as other metal oxides supported on ZrO 2 and Cu-and Fe-based zeolite catalysts. The average particle sizes of RhO x in RhO x /ZrO 2 at Rh loadings of 1, 5, 10, and 15 wt % were 1.5, 1.9, 2.0, and 2.5 nm, respectively. According to the catalytic decomposition rate per Rh used, the loading amount of Rh species has a significant impact on the efficiency of N 2 O decomposition, with the optimal Rh loading being 10 wt % (Rh metal basis). The apparent activation energy (E a ) for the catalytic decomposition of N 2 O over RhO x /ZrO 2 with 10 wt % Rh was 111 kJ mol −1 , which is almost the same as that for bulk Rh 2 O 3 (110 kJ mol −1 ). These results suggest that the RhO x species in relatively large particles serve more effectively as catalytically active sites compared to those in particles smaller than 1.5 nm. Moreover, kinetic studies and in situ/operando X-ray absorption spectroscopy studies revealed that the reaction is mediated by the redox cycles of the RhO x species, during which N 2 O acts as an oxidizing agent to fill the oxygen vacancies that are created upon heating with concomitant formation of molecular O 2 .