Graphene-filled epoxy composites have recently attracted much concern in electronic industries. However, graphene can cause sharp diminishment on the electrical resistivity of such composites. To date, electrically insulative alumina nanoparticles are chosen as a secondary filler to isolate the graphene sheets. In the present study, reduced graphene oxide (RGO) was prepared and characterized with FTIR, XRD, Raman spectroscopy, TEM, and AFM analysis. Thereafter, RGO and alumina were dispersed at different hybrid ratios of 10:0, 8:2, 6:4, 5:5, 4:6, 2:8, and 0:10 by ultrasonication into the epoxy matrix at a fixed loading of 1 wt%. Accordingly, the thermal, electrical and mechanical properties of the hybrid epoxy nanocomposites were investigated to achieve the best performance. Based on a decision-making technique, the synergy of RGO and alumina at 6:4 was considered to be the best. At 6:4, the thermal …