A Fe–Al intermetallic layer was formed on the surface of T91 heat-resistant steel by a molten aluminum hot-dipping and heat diffusion treatment. It is shown that the layer was composed of Al, FeAl 3 and Fe 2 Al 5 phases in the as-dipped state while only Fe 3 Al phase retained after the heat treatment. The intermetallic layer exhibited typical columnar grain structure after the heat treatment, and the thickness of aluminizing layer was increased from 55μm at 760°C to around 100μm at 1050°C heat treatment. Such a phase composition and grain morphology are favorable for the oxidation and corrosion resistance of T91 steel.