Effect of reaction conditions were investigated for Fischer-Tropsch (FT) synthesis process over Fe/Cu/K./SiO₂ catalyst for maximization of a selective range of liquid hydrocarbon (C₅₋₂₀). Operating conditions of the reaction have a strong impact on the activity and selectivity of the process. The parametersthat influence the FT synthesis reaction and product distribution include the reactor temperature, pressure,space velocity, the H₂/CO molar ratio in the feed syngas and the catalyst. Experiments were performed at varying range of temperature, pressure, Space velocity and H₂/CO molar ratio. Variation inC₅₊ selectivity and (olefin/paraffin) O/P ratio were observed and analyzed to select the optimum values. Reaction conditions affect the H₂and CO surface coverage and re-adsorption of olefins which play a crucial role in altering overall product selectivity. Reaction rates for FT and water gas shift (WGS) reactions were compared at different conditions. At optimum conditions, CO conversion and C₅₊ selectivity were 45.9% and 77.4%, respectively.