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An Al2O3-modified chromizing coating was produced by chromizing as-electrodeposited Ni-Al2O3 nanocomposite film using pack cementation method at 1100 oC for 3 h. For comparison, the chromizing was also performed in the same condition on as-deposited Ni film without Al2O3 nanoparticles. SEM/EDAX and TEM results indicate that the co-deposited Al2O3 nanoparticles are homogeneously dispersed in the finer-grain nanocrystalline Ni grains. At the same time, the co-deposited Al2O3 nanoparticles restrain the grain growth during chromizing by anchoring the movement of grain boundaries, which leads to the formation of finer grained chromizing coating. It is indicated from oxidation at 900 ℃ for 120 h that although both two chromizing coatings grow chromia scales during oxidation, the Al2O3-modified chromizing coating exhibits an increased oxidation resistance due to the accelerated chromium diffusion to the oxidation front via the increased grain boundaries and consequently accelerated the formation of a continuous chromia layer in a shorter transient time, together with the change of the oxidation mechanism. The effect of Al2O3 on the microstructure and oxidation of the chromizing coatings are discussed in the detail