A one-step method for the preparation of polystyrene (PS)-functionalized graphene nanosheets, homogeneously dispersed in a PS matrix and forming electrically conductive graphene/PS nanocomposites, via in situ peeling of graphite nanoplatelets into graphene nanosheets in the presence of a PS solution, is presented in this paper. The resulting PS-functionalized graphene sheets displayed a fluff-like nano-structure. The backbones of PS stacked onto the basal plane of graphene sheets under strong π–π interactions with the grafted ratio up to 85 wt%. The chains of PS could effectively prevent the graphene sheets from aggregating and the prepared graphene/PS nanocomposites, with homogeneously dispersed mono- and few-layer graphene, exhibit an extraordinary electrical property, with a percolation threshold of about 2.7 wt%, far outstripping the starting graphite or carbon black as counterpart.