Noncovalent functionalization was used to modify the graphene nanosheets via pi-pi stacking of pyrene-terminated molecule (Py-LC), resulting in an intercalated layer structure incorporated with about 45 wt% of Py-LC. The organically modified graphene (Py-LC-rGO) has a better dispersion in the PET matrix compared with that without modification. Consequently, it remarkably accelerates the crystallization of PET. Moreover, the nucleation ability of Py-LC-rGO is even stronger than that of commercial nucleation agent, sodium benzoate, leading to a thicker lamellar crystals and denser stacking of lamellae. Accordingly, the impact toughness of such a composite is improved to be nine times as that of neat PET, which can be a promising candidate as nanofiller for PET.