Abstract The catalytic performance of Ba-doped rare earth oxides prepared by a co-precipitation method for the direct decomposition of NO was investigated. Although rare earth oxide catalyzed NO decomposition reaction, their activities were significantly increased by addition of Ba. Ba-Dy2O3, Ba-Sm2O3 and Ba-Y2O3 showed relatively high catalytic activity. CO2-TPD measurements of Ba-doped rare earth oxides revealed that Ba species supported on rare earth oxides with moderate strength of basic sites, such as Dy2O3, Sm2O3 and Y2O3, can be highly dispersed on the surface of support oxide, suggesting that highly dispersed Ba species acts as catalytically active sites for NO decomposition. Although the formation of nitrite (NO2−) species during NO decomposition reaction over Ba-Dy2O3 and Ba-La2O3 was confirmed by in situ FT-IR spectroscopy, NO-TPD measurements suggested that the formation of N2 does not occur by the decomposition of adsorbed NOx species. Isotopic transient kinetic analysis performed using 14NO and 15NO revealed that the surface reaction of adsorbed species, probably NO2−, as an intermediate with other NOx adspecies is a key step for the formation of N2. Highly dispersed Ba species was considered to play an important role for the formation, adsorption, stabilization and subsequent reaction of NO2− species in NO decomposition.