The oxidation behavior of a newly designed Co–Ni-based alloy with varied addition of Ti (1.4 and 2.1 wt.%, hereafter referred as 1.4Ti and 2.1Ti alloys) was explored in air at 900 °C. It is found that an outer oxide layer composed of CoO, an intermediate oxide layer composed of intermittent TiO₂ plus continuous Cr, W-rich oxides, and an inner oxidized region composed of Al₂O₃ were formed on the surface of 1.4Ti alloy, whereas the oxide structure of 2.1Ti alloy was composed of CoO as the outer oxide layer, continuous TiO₂, Cr₂O₃, and WO₃ as intermediate oxide layer, and Al₂O₃ as the inner oxidized region. With increasing Ti content, continuous TiO₂ films formed in the intermediate oxide layer, which would lead to the formation of compact Cr₂O₃ and improved oxidation resistance after 100 h oxidation at 900 °C. These observations indicated that Ti addition can improve the high-temperature oxidation resistance of Co–Ni-based alloys.