Steelmaking slag was leached in organic-inorganic composite medium composed of acetic acid and tributyl phosphate. The main existing form and phase distribution of iron in the leached slag were investigated by combination of SEM, EDS, XPS and FT-IR. The results show that the iron phases in raw slag include elemental iron, iron oxide, ferrite and RO phase, while in the leached slag there are iron oxides and iron hydroxides, 88.9% in the form of Fe3+ and 11.1% in the form of Fe2+. The iron resource could be recovered from the leached steelmaking slag by further magnetic separation.