Iron sulfide catalysts supported on various carbon materials, on alumina and on silica were compared for their thiophene hydrodesulfurization (HDS) activity measured in a flow micro reactor at atmospheric pressure. The iron content was varied from 0.2–5.0 iron atoms per nm2 support surface area. Mössbauer spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the nature and dispersion of the iron phases present in oxidic and sulfided catalysts. Within the surface loading range studied, carbon-supported iron sulfide catalysts are much more active for thiophene HDS than the alumina- and silica-supported ones. The activity of sulfided iron on alumina catalysts was found to be even lower than expected on the basis of data obtained earlier for other (supported) transition metal sulfides. This is most likely caused by an incomplete sulfidation. Among the various carbon supports employed, activated carbons, despite their high degree of micro porosity are more suitable than carbon blacks and carbon black composites. Based on a comparison of the effective Debye temperature derived from Mössbauer data with dispersions also obtained from Mössbauer measurements on oxidic catalyst precursors, the interaction between the iron-containing phase and the various carbon supports is described in a qualitative way.