An effective approach is reported toward the reduction of weakly exfoliated graphite oxide (WEGO) using Grignard reagent of PhMgBr as both a reducing agent and a chemical functionalizer. Graphene sheet (GS) reduction with 4 mass equiv of PhMgBr showed excellent electrical conductivity of 2.5 X 10(4) S/m because the pi-pi conjugated system among GS increased the electron transfer. The 2.5 wt % GS with 4 equiv of PhMgBr reduction was used as a filler to modify poly(p-phenylene sulfide) (PPS), and the prepared GS/PPS composites displayed higher electrical conductivity (10.5 S/m) and better mechanical properties (tensile strength 88.9 MPa and Young's modulus 740 MPa) without much loss in the elongation at break. The reinforcing effects and high electrical conductivity could be explained by both the directional homogeneous dispersion of GS within the PPS matrix and the pi-pi conjugated interaction arising from the similar structural characteristics between GS and the PPS matrix.