Co/SiO2 catalysts were prepared by the incipient wetness method using the aqueous Co nitrate solution modified with various organic acids and/or chelating agents followed by drying and calcination. After H-2 reduction at 773 K, the catalyst prepared with nitrilotriacetic acid (NTA) showed Fischer-Tropsch synthesis (FTS) activity ca. 3 times higher than the catalyst without additives under mild reaction conditions (503 K, 1.1 MPa).