Fischer-Tropsch synthesis was carried out over precipitated iron-based catalysts with different amounts of CO2 in the feed stream while maintaining both total reaction pressure (1.5 MPa) and partial pressure of H-2 + CO (0.75 MPa) using an inert balance gas, N-2. The CO2 in the feed stream decreased the rate of hydrocarbon formation, but it had no significant influence on the carbon number distribution of hydrocarbons. The CO2 in the feed stream also suppressed CO2 formation, decreasing both CO conversion and CO2 selectivity. We attribute the decreased reaction rate to the partial competition in the adsorption behavior between CO and CO2 as revealed in the temperature-programmed desorption.