Thermal conductivities of epoxy composites consisting of carbon fiber (CF) and particulate silicon carbide (SiC) fillers were investigated. Composites composed of both fillers were found to have a higher packing density according to a void volume, than composites composed of either single filler on its own. The thermal conductivities were measured using a laser flash method. The CF- epoxy composite exhibited a higher thermal conductivity than SiC-epoxy composite for a filler loading of 80 wt%. The thermal conductivity of a mixed-filler composite containing 30% CF and 50% SiC by weight was found to be 10.6 W/mK, which is twice the value of that of a CF-epoxy composite, six times greater than that of a SiC-epoxy composite, and approximately 48 times greater than that of unmodified epoxy resin. This increased thermal conductivity is due to the fibrous and particulate morphologies of the fillers, which bring about an increase in the number of contact points throughout reducing void volume and increasing dispersibility of carbon fiber, thus resulting in an improved heat transfer path.