The sphericity, specific surface area, oxygen content, surface oxygen state, and high temperature oxidation characteristics of nickel-based superalloy powders with various particle sizes were studied. The oxygen absorption characteristics of the alloy powder at room temperature and the oxidation characteristics at high temperature were obtained. The argon atomized powders were sieved into different sizes of <30 mm, 30~49 mm, 50~60 mm, 61~73 mm, and 74-105 mm. The results show that the powders with size of 61~73 μm have the lowest average sphericity, minimum specific surface area, and lowest oxygen content. The powders with size of 30~49 μm have the highest average sphericity and specific surface area. However, the powder less than 30 μm has the highest oxygen content. The high-temperature oxidation process of powders at 950 ℃ can be defined as two stages: the initial stage of oxidation (0~12 h) and the later stage of oxidation (＞12 h). At the initial stage of oxidation, a dense mixed oxide layer of NiO, Cr2O3 and TiO2 was formed on the powder surface. After 12 hours oxidation, the mixed oxide layer peels off and the oxidation resistance begins to fail. After 24 hours oxidation, the mixed oxide layer peels off obviously and exposes the substrate, resulting in complete failure of oxidation resistance. After 100 hours oxidation, the powder was mainly oxidized into NiO and no obvious oxide layer exists on the surface.