Abstract: In order to investigate the high temperature creep properties of nanoparticle reinforced aluminum matrix composites, the nano Al₂O₃/6063Al composites with different Al₂O₃ volume fractions (5%, 7%) were fabricated by in-situ synthesis technology via 6063Al-Al₂(SO₄)₃ system assisted by ultrasonic chemistry. The high temperature creep tensile test was used to test the high temperature creep property of the prepared composites. XRD, OM, SEM and TEM were used to analyze micromorphology of the composites. The results show that with the help of the high-intensity ultrasoniy, the prepared Al₂O₃ reinforced particles mainly exhibit spherical or nearly hexagon shape with the size range from 20 to 100 nm, where the size refinement and dispersion uniformity of reinforced particles are elevated significantly. The apparent stress exponent, apparent activation energy and threshold stress value of nano Al₂O₃/6063Al composites increase gradually with the volume fraction increasing of reinforcement, and greatly compared with those of the corresponding matrix. The nano Al₂O₃/6063Al composites exhibit a significant improvement in creep resistance. The true stress exponent of nano Al₂O₃/6063Al composites is 8 and indicates that the creep mechanism of composites is in accordant to the substructure invariant model, i.e., controlled by the lattice diffusion. The high temperature fracture surface morphology of the nano Al₂O₃/6063Al composites indicates a brittle fracture of the composite and exhibits transcrystalline fracture under high stress condition, intergranular fracture and voids at grain boundary under low stress condition. The main strengthening mechanisms of nano Al₂O₃/6063 Al composites are dislocation strengthening and dispersion strengthening.