Fischer-Tropsch synthesis (493 K, 0.62 MPa CO, 1.24 MPa H-2) has been performed over monometallic and bimetallic Co and/or Fe clusters deposited on mesoporous silicas (HMS and SBA-15). Catalysts have been prepared by incipient wetness impregnation and characterized by N-2 adsorption-desorption isotherms, X-ray diffraction (XRD), H-2-temperature programmed reduction (H-2-TPR), and transmission electron microscopy (TEM). HMS supported Co-Fe catalyst showed the highest activity and C5+ hydrocarbon selectivity, while Co-Fe/SBA-15 catalyst revealed the highest selectivity to alcohols. Both bimetallic catalysts were more active toward the C-2-C-4 hydrocarbon fraction, with an enhancement in the selectivity to C-2(=), C-3(=) and 1-C-4(=) olefins. Both bimetallic catalysts showed greater chain growth probability values than the monometallic iron based catalysts although their performance in catalytic tests were more close to the iron catalyst. (C) 2012 Elsevier B.V. All rights reserved.