Metal-organic chemical vapour deposition of thin amorphous films of Al2O3 on steels was performed at low pressure. Aluminium tri-sec-butoxide (ATSB) was used as a precursor. The effects of the deposition temperature (200–380 °C), the deposition pressure (0.17–1.20 kPa) and the ATSB concentration ((5.5−33.5) × 10−4 kPa) were studied with respect to the growth rate of the coating and the sulphidation properties at high temperatures. The sulphidation experiments were performed for 70 h at 450 °C in a gas atmosphere consisting of 1% H2S, 1.5% H2O, 19% H2, Ar balance. From the results and scanning electron microscopy observations the best process conditions were determined.