Epoxy composites are mostly used for electronic packaging to dissipate large heat flux. Therefore, the development of highly thermal conductive but electrically insulative epoxy composites is of great importance. Here hybrid epoxy composites with improved thermal conductivity were successfully prepared by incorporating poly(ether sulfone) (PES) and SiO2-coated expanded graphite. The aim of the addition of a small amount of PES was to form the matrix via a phase-inverted structure, and then a thermal conductive path can be formed more efficiently by adding expanded graphite into PES firstly. The thermal, electrical and mechanical properties of the composites were measured. The thermal conductivity of the composite increased by 122% over the unfilled epoxy at 12 wt% filler loading. The composites still remained highly insulative due to the adding of PES and SiO2 coating on expanded graphite, and the toughness was also improved. Keywords: thermal conductive; graphite; pes; epoxy