CH3-modified Co/Ru/SiO2 catalysts were prepared and the catalytic performances for Fischer-Tropsch synthesis were investigated. The modified and unmodified catalysts were characterized by FT-IR, N-2 physisorption, TG, XRD, TPR and DRIFTS. FT-IR indicated an effective surface organic modification. TG suggested that modified catalysts had good thermal stability. XRD and TPR showed that modified catalysts had similar reducibility and CO3O4 particle size with unmodified catalyst. During reaction tests in a fixed bed reactor it was found that compared with unmodified Co/Ru/SiO2 catalyst CH3-modified Co/Ru/SiO2 catalysts showed higher selectivity to C-5-C-11 hydrocarbons, which should be ascribed to hydrophobic surface of CH3-modified Co/RU/SiO2 catalysts. (c) 2007 Elsevier Ltd. All rights reserved.