Catalytic activity for coal liquefaction of sulfate-promoted iron oxide was investigated by a high-pressure differential thermal analysis technique and an autoclave test, It was found by X-ray photoelectron spectrometry that the main component of the catalyst was iron oxide, but this included 1.1 wt % sulfur, A particular finding from these experiments was that the catalyst showed sufficiently high activity for coal liquefaction without added sulfur and the activity was comparable to the activities of the catalyst with sulfur and FeS2 catalyst in a range of temperatures between 375 and 450 degrees C. This was very interesting because the sulfate-promoted iron oxide catalyst showed significantly high activity without addition of a promoter, To find possible reasons, temperature-programmed desorption profiles of hydrogen (TPRD) of these catalysts were measured, The sulfate-promoted iron oxide catalyst showed clear TPRD profiles in a wide range of temperatures between 100 and 350 degrees C. In contrast, FeS did not show any TPRD profile, However, after oxidation of FeS with air at elevated temperatures, it did show TPRD profiles, although these were weak, This suggests that surface-sulfate species can activate hydrogen molecules. It is well-known that sulfur or sulfides are easily oxidized with water or air. It is also well-known that much water is included in the coal liquefaction system, Therefore, the catalysts used in coal liquefaction are always exposed to oxidative agents in the reaction system, Therefore, it was concluded that an active site in working states for coal liquefaction was sulfate species formed during the process on the surface of the iron-based catalysts in the coal liquefaction.