Co/SiO2 catalysts were prepared by a stepwise impregnation of aqueous solutions containing Co nitrate or chelating agent, nitrilotriacetic acid (NTA) or trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CyDTA), with various concentrations of Co2+ and the chelating agent. Fischer-Tropsch synthesis activity of Co/SiO2 catalysts having Co loadings of 5-20 mass% as metallic Co was improved by the stepwise impregnation method with these chelating agents. The catalyst prepared with CyDTA (Co loading = 20 mass%, Co2+/CyDTA = 4 mol mol(-1)) yielded 1,500 and 815 g kg-cat(-1) h(-1) of C5+ and C10-20 hydrocarbons at 503 K and 1.1 MPa, respectively, which was much greater than that with the catalyst prepared from the aqueous solution containing both Co nitrate and NTA.