Abstract: Nano-Al₂O₃/epoxy, phenolphthalein polyaryletherketone (PAEK)/epoxy and nano-Al₂O₃/PAEK/epoxy composites were prepared by mechanical mixing process. The tensile modulus, tensile strength, fracture toughness and thermal stability of the composites were comparatively studied. The results indicate that both nano-Al₂O₃ and PAEK are homogeneously dispersed in the epoxy martix. In the case of nano-Al₂O₃/epoxy composites, with the increase of nano-Al₂O₃ content, the tensile modulus increases monotonously, and the tensile strength increases first then decreases. In the case of PAEK/epoxy composites, the tensile modulus decreases slightly, and the tensile strength does not change significantly. In the case of nano-Al₂O₃/PAEK/epoxy ternary composites, the tensile modulus and the tensile strength show non-monotonous changes. Both nano-Al₂O₃ and PAEK can toughen the epoxy more or less. The toughening effect of the ternary composites is more obvious, and the combination of nano-Al₂O₃ and PAEK exhibits synergistic toughening effect. The high content nano-Al₂O₃ lowers the initial decomposition temperature of epoxy, while the other fillers improve the thermal stability of epoxy slightly. The glass transition temperature of the epoxy resin is found to be depressed with the fillers.