Within decades of development, carbon nanomaterials such as carbon black, fullerene, carbon nanotube, carbon nanofiber, graphene and their combined nanofillers have been tremendously applied in polymer material industries, generating a series of fascinating multifunctional composites in the fields from portable electronic devices, sports, entertainments to automobile, aerospace and military. Among the various material properties of the composites, electrical conductivity and mechanical performance are the two most important parameters for evaluating the effectiveness of nanofillers in the polymer matrices. In this review, we focus on the electrical and mechanical properties of diverse dimensional carbon nanofillers (e.g., zero-, one-, two-, three-dimensional nanofillers or their combinations)-reinforced polymer composites to seek the most efficient and effective approach to obtain high-performance polymeric nanocomposites.