Abstract:  The effect of high temperature carburization on the catalytic performances over an ultrafine Fe-Mn catalyst was investigated. The surface area of the catalyst distinctly decreased after carburization. The carburization process favored the formation of FeO-MnO spinel phase and α-Fe, and small iron carbide crystallite was also formed. The catalyst after carburization exhibited high light olefin selectivity and low methane selectivity during CO hydrogenation, also, the chain propagation ability was promoted. The characterization of the catalyst indicated that the surface properties of the catalyst after carburization were improved. The carburization process enhanced the basicity of the catalyst and suppressed the secondary reactions of hydrogenation, and resulted in high selectivity to light olefins.