The synthesis of trimetallic catalysts was carried out by changing each of the active metals and adding a similar metal for the hydrodesulfurization process. The roles of tungsten along with molybdenum and cobalt in addition to nickel were studied. Six trimetallic catalysts containing different metal ratios were synthesized. The activities of trimetallic and bimetallic catalysts have also been studied. TPR, mapping, FESEM, BET, ICP, XRD and TPR analyses have been used for the chemical and physical evaluation of the synthetic catalysts. A feedstock containing 11500 ppm of sulfur was used in the hydrodesulfurization process at the temperature of 340 degrees C, pressure of 65 bar and H-2/hydrocarbon volume ratio of 250. Decrease of MoO3/(WO3+ MoO3) ratios results in the better performance of the NiMoW trimetallic catalysts. No significant variations are observed in the catalytic performance of NiCoMo trimetallic catalysts. The maximum desulfurization appears to occur using high CoO/(NiO + CoO) ratio and low MoO3/(WO3+ MoO3) ratio.