An Al₂O₃/Al-Cu-Mn composite was fabricated using a combination of ball milling and liquid-solid reaction, with a nominal composition of Al-4Cu-0.5Mn-2.8γ-Al₂O₃. The composite contains reinforcement particles, including nano-sized θ’ and T(Al20Cu2Mn3) particles after T6 heat treatment, as well as in-situ synthesized nano-sized γ-Al₂O₃ particles. Tensile tests of the Al-4Cu-0.5Mn-2.8γ-Al₂O₃ composite and the Al-4Cu-0.5Mn base alloy after T6 treatment were carried out at room temperature and elevated temperatures (200 °C, 300 °C, and 400 °C). Compared with the base alloy, the yield strength of the  Al-4Cu-0.5Mn-2.8γ-Al₂O₃ composite after T6 treatment increases significantly from 187 MPa to 263 MPa at room temperature. Simultaneously, at elevated temperatures, the yield strength is also enhanced, with a yield strength of 52 MPa at 400 °C for this composite. The in-situ fabricated γ-Al₂O₃ particles, mainly distributed along the grain boundaries, are supposed to play the main strengthening role, especially at high temperatures. This work acts as a reference for designing composites for high-temperature applications.