Epoxy-based composite films are fabricated by film-casting and thermal-curing of epoxy resin/hardener mixtures with 5.0wt% mixed carbon fillers of different compositions of graphene and MWCNT. The electrical resistivity of the composite films decreases from ∼103 to ∼102Ωcm with increasing the MWCNT composition in the mixed carbon fillers, which results from the bridge effect of MWCNTs among graphene sheets. Accordingly, maximum temperature of the composite films attained at an applied voltage increases with the MWCNT composition in the hybrid carbon fillers. The composite films exhibit excellent electric heating performance in terms of temperature response rapidity and electric power efficiency.