Abstract: Alumina (Al₂O₃) was modified by the silane coupling agent γ-aminopropyltriethoxysilane (KH550) and then added into high density polyethylene/polyamide 6 (HDPE/PA6) blend to improve the thermal conductivity of the composites. The modification of Al₂O₃ was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TG). The thermal conductivity, heat resistance, tensile properties and the morphology of the composites were investigated by using thermal conductivity detector, Viscat softening temperature tester, universal testing machine and scanning electron microscope. The results indicate that the thermal conductivity of the composites increases gradually with the increasing of the filler content. The heat resistance and Young's modulus are also improved after the addition of Al₂O₃. The modified Al₂O₃ (m-Al₂O₃) can further improve the thermal conductivity, heat resistance and Young's modulus of the composites compared with unmodified Al₂O₃.