High temperature oxidation of nickel has been studied at 1373 K in atmospheres, at oxygen partial pressures between . The oxidation kinetics have been followed by continuous mass gain measurements using a thermobalance at the oxidation temperature and by measurements of the scale thickness in metallographic cross sections, after cooling. The grain growth of during oxidation has been also investigated. A double‐layered scale is formed near platinum markers, although only a single scale is observed away from the markers. The outer layer is identical in thickness to the scale formed away from markers, and the growth rate is controlled by the outward diffusion of nickel ions. The diffusivity of nickel ions is proportional to at oxygen partial pressures higher than ≈10 Pa. The oxygen pressure dependence of the diffusivity indicates that the predominant defect is a doubly‐charged nickel vacancy. At oxygen partial pressures lower than ≈10 Pa, the oxygen pressure dependence becomes smaller, suggesting extrinsic behavior. The formation of the inner layer is explained, assuming the inward oxygen transport along grain boundaries in the outer layer. The size of the oxide grains, away from markers, is almost the same as that of the nickel substrate, but the oxide near the markers is much smaller. Grains near the markers coarsen, and the cube of the grain size is proportional to time, and the rate constant is also proportional to .These results suggest that grain growth proceeds through the pore drag mechanism, and that the rate is determined by the lattice diffusion of nickel ions.