The isothermal oxidation behavior of Ni–20Cr alloys with 0–3.0 mass% of Ti was investigated in air in the temperature range from 1273 to 1473 K . Ti addition apparently increased the oxidation rate of the Ni–20Cr alloy. The scale formed on the Ni–20Cr–xTi alloys consisted of an outer NiO layer and an inner Cr₂O₃ layer. The growth rate of the Cr₂O₃ layer increased with increasing Ti content, while that of the NiO layer remarkably decreased. The spallation of the scale and the surface topography of the scale were also markedly affected by the Ti addition. The spalled scale was fine powders in the case of the alloys with smaller amounts of Ti, but the size of the spalled scale increased with increasing Ti content of the alloy. Crystals of the scale significantly grew up with increasing Ti content of the alloy at 1473 K . The surface topography of the Ni–20Cr alloy with 3.0% Ti showed a faceted structure. EPMA observation revealed a remarkable accumulation of Ti in the scale, which seemed to result in an increase in the vacancy concentration of the scale due to altering of the defect structure of the scale. An increase in the vacancy concentration of the scale was considered to enhance the oxidation rate of the alloy and the sintering of the scale.