The relatively low strength of aluminum (Al) alloys and Al matrix composites at high temperatures has greatly limited their applications in aerospace and automobile areas. In this study, high-performance carbon nanotubes (CNTs)/Al composites with high room-temperature tensile strength over 500 MPa were tested at elevated temperatures up to 400 °C. Results showed that the strength of CNTs/Al composites increased with increasing CNT content up to 5 vol%. CNTs/Al composites showed improved reinforcing effects at elevated temperatures compared with those at room temperature. Consequently, the 5 vol%CNTs/Al composite achieved high tensile strength of 205 MPa when tested at 400 °C, which was superior to those values (less than 100 MPa) of most available Al matrix composites. The underlying mechanism was thoroughly discussed from the grain sizes, phase compositions, interface reaction and strengthening mechanisms at different testing temperatures. The results have revealed the excellent high-temperature properties of CNTs/Al composites and their potential use at elevated temperatures. Display omitted •CNTs could mitigate the strength deterioration in composites at high temperatures.•The thermal stability of CNTs/Al composite was higher than Raw Al and BM Al.•The ultimate tensile strength of CNTs/Al composite achieved 205 MPa at temperature 400 °C.•CNTs reinforcing effect at high temperatures was superior to other reinforcement.