Iron/carbon (Fe/C) nanocomposite catalysts are prepared for Fischer-Tropsch synthesis reaction. A preparation method includes steps of mixing iron hydrate salts and a mesoporous carbon support to form a mixture, infiltrating the iron hydrate salts into the carbon support through melt infiltration of the mixture near a melting point of the iron hydrate salts, forming iron-carbide particles infiltrated into the carbon support through calcination of the iron hydrate salts infiltrated into the carbon support under a first atmosphere, and vacuum-drying the iron-carbide particles after passivation using ethanol. Using such catalysts, liquid hydrocarbons are produced.