A Ni-La2O3 composite film has been developed by coelectrodepostion of La2O3 particles with Ni onto pure Ni surfaces. An investigation by a high-resolution electron microscope (HREM) revealed a dispersion of La2O3 nanocrystallites (below 5 nm) in the as-codeposited film. Isothermal (at 900 and 1000 degrees C) arid cyclic (at 1000 degrees C) oxidation in air showed a significantly slower growth rate and a noticeably higher cracking resistance for NiO scale on Ni-La2O3-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 similar to 15 smaller than that on the La2O3-free specimens. Electron probe microscope analysis indicated that La2O3 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 La2O3-doped NiO scale. It is therefore proposed that the rapid outward diffusion of Ni along short-circuit paths in the La2O3-modified NiO layer may be inhibited by second-phase La2O3 particles and also by segregated lanthanum ions from the dissolution of La2O3 nanoparticles which originally existed in the Ni-La2O3 codeposited film.