Abstract: Cobalt based catalysts supported on amorphous SiO₂ were prepared through thermal decomposition as well as incipient wetness impregnation. They were characterized by means of TG, XRD, TEM and TPR and used in Fischer-Tropsch (F-T) synthesis. The results indicated that Co/A200-I catalyst prepared by impregnation exhibits high F-T synthesis activity, though cobalt particles in it are in irregular shape. In comparison, the cobalt particles in Co/A200-D catalyst prepared through decomposition are in secondary spherical structure with relatively uniform diameter and the Co/A200-D catalyst exhibits high selectivity to light hydrocarbon in F-T synthesis. The specific surface area of SiO₂ support also influences the structure of catalysts obtained. Compared with the Co/A200-D catalyst, Co/A380-D catalyst prepared by decomposition with higher surface area support is more difficult in reduction due to the stronger metal-support interaction; however, Co/A380-D exhibits higher catalytic activity in F-T synthesis, probably due to the higher cobalt dispersion