The formation of carbon dioxide in the Fischer-Tropsch synthesis performed in a three-phase system in the presence of a nanosized catalyst was studied. The synthesis temperature was found the main parameter responsible for the yield of CO2. At a constant conversion of CO, pressure has almost no effect on selectivity for the formation of CO2, whereas a decrease in the H-2/CO ratio and an increase in the contact time or the concentration of an active component in the reaction zone lead to a decrease in the selectivity.