Fischer-Tropsch synthesis was carried out in slurry phase over uniformly dispersed CO-SiO2 catalysts prepared by the sol-gel method. When 0.01-1 wt.% of noble metals were added to the CO-SiO2 catalysts, a high and stable catalytic activity was obtained over 60 h of the reaction at 503 K and 1 MPa. The addition of noble metals increased the reducibility of surface Co on the catalysts, without changing the particle size of Co metal significantly. High dispersion of metallic Co species stabilized on SiO2 was responsible for stable activity. The uniform pore size of the catalysts was enlarged by varying the preparation conditions and by adding organic compounds such as N,N-dimethylformamide and formamide. Increased pore size resulted in decrease in CO conversion and selectivity for CO2, a byproduct, and an increase in the olefin/paraffin ratio of the products. By modifying the surface of wide pore silica with CO-SiO2 prepared by the sol-gel method, a bimodal pore structured catalyst was prepared. The bimodal catalyst showed high catalytic performance with reducing the amount of the expensive sol-gel CO-SiO2. (C) 2004 Elsevier B.V. All rights reserved.