A series of nanosized Fe-Mn-Cu-K composite catalysts was prepared by a supercritical combined technology. The nanosized catalysts were characterized by means of XRD, TEM and BET techniques, and tested for catalytic performance under Fischer-Tropsch synthesis (FTS) reaction conditions. The catalyst synthesized by the supercritical combined technology has some excellent properties. Additionally, the drying and crystallization of nanosize catalyst could be achieved simultaneously by this supercritical combined technology. The addition of Mn, Cu and K promoters can improve the catalytic performance properties of the catalyst, including lower CH4 and CO2 formation rates, and higher production rates of desired light-olefin. The optimal performance with a 95.7% CO conversion and a 46.5% light-olefin yield was obtained by using a catalyst component of Fe/Mn/Cu/K = 60:25:10:8.5. In summary, optimal catalytic performance was obtained by using the nanosized catalyst under supercritical reaction conditions, resulting in higher CO conversion, less byproduct CO2 formation. and a higher yield of light-olefin. (C) 2009 Elsevier B.V. All rights reserved.