Abstract In this study, NiO films with various Cu contents of 0–23.3 at.% were deposited on low alkali glass substrates, respectively, by using radio frequency magnetron sputtering at room temperature. In order to investigate thermal stability, the NiO and NiO–Cu films were post-annealed at temperatures of 50–400 °C in various atmospheres (air, O 2 and vacuum). For the pure NiO film (with no Cu content) electrical resistivity ( ρ ) did not change, if it was annealed at temperatures below 150 °C both in air and O 2 . However, ρ of the NiO–Cu films (with Cu content ≧ 18.3 at.%) remains unchanged, even if they were annealed up to 200 °C (in air and O 2 ). In a vacuum atmosphere, ρ of the NiO–Cu films (containing 18.3 at.% Cu) stayed constant only up to 150 °C. After this point, ρ decreases significantly. We believe that post-annealing the Cu-doped NiO films at higher temperatures in vacuum could result in the Cu precipitating at the grain boundaries, which leads to reduction in ρ . In addition, we also investigated the aging effect on the NiO and NiO–Cu films under the air atmosphere of 1 atm, 25 °C and 70% relative humidity condition. ρ of pure NiO films increased only slightly after aging time of 53 days. However, carrier mobility (μ) increased and carrier concentration ( n ) dropped significantly after 15 days, For the NiO–Cu films (with Cu contents ≧ 13.2 at.%), after 53-day aging time, both ρ and μ rose slowly, while n decreased slightly.