Ag promoted Co/Al2O3 Fischer-Tropsch synthesis catalysts were preparation by wetness impregnation and characterized by nitrogen physisorption, X-ray diffraction, temperature programmed technologies and H-2 chemisorption. Their performances of Fischer-Tropsch synthesis were evaluated in a fixed bed reactor. The result indicated that Ag promoter can improve the dispersion of the cobalt species and facilitate the reduction of CoO to metallic Co. Ag significantly increases the CO conversion rate and C-5(+) selectivity of Fischer-Tropsch reaction, while decreases the production of methane. However, negative effects were found at higher level Ag loading. As a result, the presence of relatively small quantities of Ag additive can help to enhance the performance of Co/Al2O3 catalysts in Fischer-Tropsch synthesis.