Fe-2Cr-1Mo steels were Aluminized by pack-cementation to protect from oxidation and corrosion. After aluminized Fe-2Cr-1Mo steels were corroded at 800 oC for 10-100 hr in (0.031 atm H2O+0.0242 atm H2S+0.9448atm N2)-mixed gas condition. The corroded test coupons were characterized by an X-ray diffractometer (XRD) with Cu-Kα radiation, a scanning electron microscope (SEM), Energy Dispersive X-Ray Spectrometer(EDS), an electron probe micro-analyzer (EPMA) and Electron Back Scatter Diffraction(EBSD). Pack-cementation resulted in the formation of Al/Al2O3 top coat outer layer and Fe-Al intermetallic compound inner coat layer on the matrix. The Fe-Al intermetallic compound inner coated layer consisted primarily of a wide, long FeAl and Fe3Al phase. When corroded at 800 oC for 10-100 hr, the Al/Al2O3 top coat outer layer formed on the aluminized steel protected the Fe-2Cr-1Mo steel against corrosion. Uncoated Fe-2Cr-1Mo steel formed a thick, fragile, and non-protective FeS scale.