Understanding the interfacial structures and energetics of interfaces between γ-Al₂O₃ phase and Al matrix is critical to understanding the stabilities of the γ-Al₂O₃ film during oxidation of Al. Here we report a comprehensive first-principles investigation on the structures and energetic properties of interfaces between the metastable γ-Al₂O₃ phase and Al. 19 interfacial structure models are constructed by considering two spinel and one nonspinel γ-Al₂O₃ models proposed by Ouyang, Pinto and Digne, respectively, the possible orientation relationships with Al and different interfacial terminations. We find that the Pinto model with (001)_γ||(111)_Al orientation relation shows the lowest interfacial energy of 1.08 J/m², which is attributed to the regularly distributed out-of-plane Al-O interfacial bonds. The work of separation is directly related to the strength and density of the interfacial bonds. Our calculations provide the necessary interfacial structures and energetics for predicting the stabilities of the γ-Al₂O₃ film during oxidation of Al.