A composite film has been developed by coelectrodepostion of particles with Ni onto pure Ni surfaces. An investigation by a high‐resolution electron microscope (HREM) revealed a dispersion of nanocrystallites (below 5 nm) in the as‐codeposited film. Isothermal (at 900 and 1000 °C) and cyclic (at 1000 °C) oxidation in air showed a significantly slower growth rate and a noticeably higher cracking resistance for NiO scale on ‐coated Ni than on Ni, and Ni with an electrodeposited film of pure Ni. Moreover, the grain size of the nickel oxide on the composite film was a factor of 6 ∼ 15 smaller than that on the ‐free specimens. Electron probe microscope analysis indicated that dispersed in the outer part of the NiO scale after the codeposited film has been oxidized completely. An analytical transmission electron microscope revealed that La segregated to the grain boundaries of the ‐doped NiO scale. It is therefore proposed that the rapid outward diffusion of Ni along short‐circuit paths in the ‐modified NiO layer may be inhibited by second‐phase particles and also by segregated lanthanum ions from the dissolution of nanoparticles which originally existed in the codeposited film.