Abstract: Mn_1.56Co_0.96Ni_0.48O_4±δ (MCN) spinel thin films were fabricated by annealing Mn-Co-Ni ternary alloy films at different O₂ pressures. Effects of oxygen nonstoichiometry on MCN films were investigated. As oxygen pressure increase from 10 kPa to 90 kPa, the crystallinity of the MCN films was improved; the absorbed oxygen decreases from 61.6% of surface O at 10 kPa to 29.2% at 90 kPa of it; and the room temperature resistance quickly decreases from 183.0 MΩ to 6.9 MΩ. The optical absorption of the MCN films suggest that the concentration of Mn cation increases with the increase of oxygen partial pressure correspondingly during annealing improved correspondingly.