The formation of the Fe-Al inhibition layer in hot-dip galvanizing is a confusing issue for a long time. This study presents a characterization result on the inhibition layer formed on C-Mn-Cr and C-Mn-Si dual-phase steels after a short time galvanizing. The samples were annealed at 800 ℃ for 60 s in N2-10% H2 atmosphere with a dew point of -30 ℃, and were then galvanized in a bath containing 0.2 %Al. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) was employed for characterization. The TEM electron diffraction shows that only Fe2Al5 intermetallic phase was formed. No orientation relationship between the Fe2Al5 phase and the steel substrate could be identified. Two peaks of Al 2p photoelectrons, one from metallic aluminum and the other from Al 3+ ions, were detected in the inhibition layer, indicating that the layer is in fact a mixture of Fe2Al5 and Al2O3. TEM/EDS analysis verifies the existence of Al2O3 in the boundaries of Fe2Al5 grains. The nucleation of Fe2Al5 and the reduction of the surface oxide probably proceeded concurrently on galvanizing, and the residual oxides prohibited the heteroepitaxial growth of Fe2Al5.