The Fischer-Tropsch (FT) synthesis reaction was conducted using bimodal catalyst in a slurry phase reactor. The bimodal catalyst was prepared from a bimodal support which was tailor-made by introducing SiO2 sol directly into the large pores of a SiO2 gel pellet The bimodal catalyst exhibited significantly higher activity in the slurry-phase Fischer-Tropsch synthesis than in other unimodal catalysts. The support with a large surface area allowed a highly dispersed cobalt particle, and its large pore size improved the diffusion of reactants and products. The diffusion of reactants inside the catalyst pores was simulated, and the effects of pore structure and pore size on catalytic performances were consistent with the simulation results. (c) 2005 American Institute of Chemical Engineers.