A bimodal iron-based catalyst was prepared by a new one-step impregnation method. The active components were used as the "brick" to directly build the small pores inside the large pores of support, which was quite different from the previous bimodal catalysts that were prepared once more on a bimodal support. Comparing with the unimodal catalysts and conventional co-precipitated catalyst, the prepared bimodal catalyst exhibited excellent activity in Fischer-Tropsch synthesis due to the improved active metal dispersion and fastened diffusion efficiency. This preparation method is much simpler than the previous methods and can be extended to prepare various bimodal catalysts with different chemical compositions. (C) 2008 Elsevier B.V. All rights reserved.