The effects of methanol on the performance of Co/SiO2 catalyst for Fischer-Tropsch synthesis were studied in a fixed-bed reactor at 210 degrees C and 2.0 MPa. It was found that external addition of methanol brought about an increase in the selectivity of methane, water and CO2 and a decrease in the activity of the catalyst. FTIR and TPSR characterizations proved that methanol first converted to the methoxy groups and water and then the methoxy groups reacted with hydrogen to produce methane, which led to the increase of the selectivity of methane and water. And the increase of the selectivity of CO2 was ascribed to the water-gas shift reaction. The decline of the activity might result from the instantaneous oxidation of the metallic cobalt due to the sudden addition of methanol and the formation of cobalt silicates and/or hydrosilicates species. More methanol introduction into the feeding gas would result in the formation of larger amount of silicates species, which led to the more serious deactivation of the catalyst. In addition, the hydrogen was found necessary for the chain propagation whereas CO was not. The methanol might substitute for CO to perform the chain initiation. (C) 2008 Elsevier B.V. All rights reserved.