To enhance the mechanical properties of Al–(La, Ce) alloys, melt spinning and hot extrusion were employed to fabricate Al-La-Mg-Mn alloy with an ultrafine-grained structure (∼0.56 μm). The as-extruded alloy exhibits the highest tensile strength of 621 ± 4 MPa among Al–(La, Ce) alloys fabricated by various methods while retaining an appreciable elongation of 6.8 ± 1.1 %. The high strength is mainly ascribed to the ultrafine grains and high-volume intermetallics, conferring robust grain boundary strengthening and Orowan strengthening effects. Additionally, this study delved into the high-temperature (400°C) coarsening behavior of the intermetallic and grain size. The findings unveil an exceptionally low coarsening rate of the intermetallic at 400°C (3.19×10−33 m4 s−1), accompanied by only slight grain coarsening, underscoring the remarkable thermal stability of the ultrafine-grained structure.