C-type cubic (Y0.99-xTbxBa0.01)(2)O2.99+delta (0 <= x <= 0.4) catalysts were prepared by coprecipitation. The NO decomposition activities at 1173 K were higher than that of (Gd0.7Y0.26Ba0.04)(2)O-2.96 reported previously. The highest catalytic activity was obtained for (Y0.69Tb0.3Ba0.01)(2)O2.99+delta, and 100% NO conversion into N-2 and O-2 was realized at 1173 K on this catalyst. Furthermore, the conversion ratio was maintained as high as 70.8% even in the presence of 5 vol % oxygen.