A 60%Fe/Al2O3catalyst was prepared by the co-precipitation method. It was reduced by H2to produce metallic Fe, which was then sulfided by CS2to Fe0.96S and Fe3S4or phosphided by triphenylphosphine (PPh3) in liquid phases to Fe2P and FeP. It was found that the iron sulfides (Fe0.96S and Fe3S4) exhibited the low activity for the hydrodesulfurization (HDS) reactions. The HDS activity was also low on the Fe(metal)/Al2O3and Fe2P/Al2O3catalysts since they were converted into Fe0.96S and Fe3S4during the HDS reactions. In contrast, the FeP/Al2O3was found to be stable and active for the HDS reactions. In particular, FeP/Al2O3possessed significantly smaller FeP particles than FeP/C, leading to the significant higher HDS activity of FeP/Al2O3than FeP/C.