Two Fe/carbon catalysts were prepared to study the influence of the intermediate iron species on the activity and selectivity in the Fischer-Tropsch synthesis (FTS). The solids were characterized by XRD, CO chemisorption, Atomic Absorption, Nitrogen Adsorption and Mossbauer spectroscopy. Using two loading of consolidant agent, two supports with different specific surface areas were obtained. The resulting catalysts showed different iron species. The catalyst with lower reduction degree produces a non-stoichiometric iron carbide during FTS, which has a higher activity and light olefins selectivity. (C) 2007 Elsevier B.V. All rights reserved.