The effects of ultrasonication and UV/ozone treatment of graphite on electrical conductivity of epoxy-based nanocomposites containing graphite nanoplatelets are investigated. Ultrasonication applied at various stages of composite fabrication enhanced the exfoliation and dispersion of graphite within the matrix. A porous multi-layer graphite structure resulted in a higher electrical conductivity and poorer mechanical properties than the completely exfoliated graphite. UV/ozone treatment improved both the electrical conductivity and mechanical properties by improving the graphite–epoxy interfacial adhesion, which is attributed to ameliorating changes in graphite surface chemistry and morphology.