Abstract: Ni promoter was introduced into the coprecipitated FeMnK/SiO2 FischerTropsch synthesis catalysts. The effects of Ni on catalyst structural properties, reduction and carburization behaviors were studied by N2 physical adsorption, XRD, Mssbauer spectroscopy, temperature programmed reduction (TPR) in H2 and CO, and isothermal reduction in syngas. The results indicate that Ni promoter increases the BET surface areas of catalysts and is favorable to the formation of smaller crystallite particles. H2TPR results show that Ni decreases the reduction temperature of catalysts, and CO-TPR results show that Ni facilitates the oxygen removal and increases the carbon introduction content. These effects contribute to a significant improvement of the reduction and carburization behaviors of catalysts in syngas, and the promotion effect increases with the Ni loading content.