Abstract: SBA-15 supports modified by different hydrophobic reagents (methyltriethoxysilane, dimethyldiethoxysilane and chlorotrimethylsilane) were prepared before the impregnation of cobalt precursor. The effects of hydrophobic modification on the crystallite structure and the reduction behaviors were studied by BET, FT-IR, ²⁹Si CP MAS NMR, XRD, and H₂-TPR. Fischer-Tropsch (F-T) synthesis performances were evaluated in a fixed-bed reactor at 2.0 MPa, 200~250 ℃, H₂/CO (volume ratio)=2, and GHSV=1 000 h^-1. The result indicated that hydrophobic modification led to the increase in reduction degree of the supported cobalt, resulting in the increase of CO conversion of cobalt catalysts for F-T synthesis. Moreover, due to the increase of Co₃O₄ crystallite size and the decrease of un-reducible cobalt compound after hydrophobic modification, CH₄ selectivity decreased and C₅₊ selectivity increased.