Abstract: The effects of K, Ru or La promoters on the structure, surface area, crystal phase, and catalytic behavior during FT synthesis of carburized and uncarburized fused Fe catalysts were studied by XRD, XPS, TPD, N₂-physisorption and catalytic reaction evaluation techniques. Addition of K improved selectivity of C₅₊ products for both the carburized and uncarburized catalysts. Addition of Ru suppressed catalytic activity of the carburized catalyst, but had little influence on the uncarburized one. Addition of La led to the encapsulation of the iron carbide, which consequently severely inhibited the carburization and decreased the activity. While Ru and La promote the formation of light components due to their ability to promote hydrogen adsorption. The performance of the reaction in the experiment indicated that the U-K catalyst had the best product distribution, in which the methane selectivity was 4.04%, and the C₅₊ selectivity was 75.84%.