The physicochemical and catalytic properties of La0.8Ce0.2Mn1-xFexO3 were studied by NO + CO activity tests and a series of characterizations. Improvement of catalytic activity for the La0.8Ce0.2Mn0.6Fe0.4O3 catalyst was related to its relatively high surface-dispersed Mn4+-O-Mn3+ and Mn4+-O-Fe3+ species, which seemed to be the primary active component. In situ diffuse reflectance infrared Fourier transform spectroscopy results suggested the following: (1) CO was oxidized by oxygen originating from Mn4+-O-Mn3+ and Mn4+-O-Fe3+ species, which could be reduced and produced surface oxygen vacancies and surface synergistic oxygen vacancies. (2) Preferential adsorption of NO on the catalyst surface produced some nitrite/nitrate species, which could be desorbed, transformed, or dissociated during heating. (3) Active sites produced by the desorption, transformation, and dissociation of nitrate/nitrite species could also be used for CO adsorption, resulting in the formation of the Fe2+-CO species, which could react with N2O. Finally, a possible reaction mechanism was suggested to further understand the NO + CO reaction.