In this paper, nitrous oxide decomposition over a series of MCO3-Co3O4 (M = Ca, Sr, Ba) catalysts having M/Co ratios of 0.1-0.4 has been studied. The various catalysts were characterized using thermal (TGA, DTA), XRD, IR and N-2 sorption techniques. N2O decomposition activity was found to be dependent on the type of the alkaline earth cation, the M/Co ratio, cobalt oxide crystallites sizes, and the calcination temperature.