A CeO₂-modified aluminide coating was prepared on 309 stainless steel by pack cementation method with NH₄Cl as activator. The surface and cross-section of the coating before and after cyclic-oxidation at 900 °C for 50 cycles were analyzed by X-ray diffractometer and scanning electron microscope coupled with energy dispersive spectroscope. The microstructure analysis results show that the modified coating consists of Fe₄Al₁₃ phase. A few CeO₂ nanoparticles are entrapped due to the outward diffusion of base metal. Compared with the normal aluminide coating without the addition of CeO₂ nanoparticles, the aluminide coating modified by dispersed CeO₂ nanoparticles has better scale spallation resistance in air at 900 °C. Some Fe₂Al₅ phases can be found on CeO₂-modified aluminide coating even after 50 cycles of oxidation. Additionally, the outward-diffused Al layer, the intermediate FeAl layer, and the external Fe₂Al₅+FeAl mixed layer exist in the coating, suggesting that CeO₂ nanoparticles can retard the degradation of aluminide coatings.