Abstract: Constructing thermal conductive pathways in polymer matrix with interconnected high conductive thermal fillers is an effective strategy to enhance the thermal conductivity of the composites. In this paper, eutectic Sn-Bi alloy (Sn₅₇Bi₄₃) nanoparticles are deposited on the surface of Al₂O₃ microspheres by coreduction method to prepare Al₂O₃-Sn₅₇Bi₄₃ hybrids as thermal conductive and electrical insulating fillers for epoxy resin. During the heat curing of epoxy resin, Sn₅₇Bi₄₃ nanoparticles on the Al₂O₃ surface melt and bridge the separate fillers together to form effective thermal conductive pathway, and thus enhance the thermal conductivity of the composites. When filler volume fraction is 60vol%, the thermal conductivity of Al₂O₃-Sn₅₇Bi₄₃/epoxy composites is 2.95 W·(m·K)⁻¹, 62.1% higher than that of Al₂O₃/epoxy composites (1.82 W·(m·K)⁻¹). The results of Fogyel and Agari simulation demonstrate that the deposition of Sn₅₇Bi₄₃ on Al₂O₃ surface reduces the thermal contact resistance between fillers and forms thermally conductive networks more easily. The Al₂O₃-Sn₅₇Bi₄₃/epoxy composites exhibit higher dielectric loss, lower dielectric strength and volume resistivity than Al₂O₃/epoxy composites, still with electrical insulating properties. What is more, the tensile strength of the Al₂O₃-Sn₅₇Bi₄₃/epoxy composites is improved, because the improved interfacial properties of filler-matrix and the formed networks could transfer stress and prevent crack expansion.