Catalysts of cobalt-cerium composite oxide doped with series of alkaline earth metals were prepared using the citrate method. Results of catalytic activity tests showed that the addition of alkaline earth metals enhanced the efficiency of N2O decomposition according to the following order: Mg<Ca<Sr,Ba. Characterization of these catalysts was done using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, X-ray photoelectron spectroscopy (XPS), oxygen temperature-programmed desorption (O2-TPD) and hydrogen temperature-programmed reduction (H2-TPR). Results indicated that the addition of alkaline earth metals did not change the crystal structures and specific surface areas of catalysts, but did enhance the electron donation ability of the active site (Co2+). The surface reaction of N2O with Co2+ involved electron donation from Co2+ to the anti-bonding orbital of N2O that resulted in the release of N2. The desorption of residual oxygen leads to the regeneration of the active site (Co2+) through the donation of electrons back to Co3+. We conclude that the addition of alkaline earth metals promotes surface reactions of N2O with Co2+ by facilitatingelectron donation from the active site. This process is the rate-determining step for purecobalt-cerium composite oxide catalysts and the catalytic activity for the decomposition of N2O is thus improved.