The relationship between NO decomposition activity or? lanthanum transition metal oxide catalysts (transition metal=Cr, Mn, Fe, Co and Ni) and their oxygen desorption properties was investigated by using catalytic activity measurements, temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and molecular orbital calculations. The NO decomposition activity correlated with both the amount of O-2 desorbed and the temperature of O-2 desorption. The variations in the temperature of O-2 desorption during TPD could be explained by electronic interaction with the transition metal. The variations in the Ols photoline observed by XPS could be explained by the variations in the charge of the surface oxygen species, which was affected by the electronic interaction with the transition metal. Molecular orbital techniques are powerful tools in NO decomposition catalyst research.