Achieving high levels of electrical and thermal conductivities in polymer composites is challenging. In this work, a hybrid filler system together with a blend matrix was used in an attempt to obtain highly conductive composites. Carbon nanotube, carbon fiber, and graphite were used as the conductive fillers with a blend matrix of polycarbonate (PC) and high density polyethylene (HDPE). Polyethylene glycol (PEG) was also used as a compatibilizer. The HDPE was used in a range of 10 – 50 wt. % of PC. CF and G were used in ranges of 10 – 30 wt. % and 30 – 50 wt. % of the composite, respectively. CNT and PEG were fixed at 3 wt. % and 1.5 wt. %, respectively. The Composites were fabricated using a twin screw extrusion system followed by compression molding. Microstructure and conductivities of the samples were investigated. The results showed that due to the preferential localization of the fillers in the blend, both electrical and thermal conductivities were significantly enhanced, compared to the composites with a single matrix of PC.