Noncovalent interactions between chemically reduced graphene oxide (rGO) and aliphatic polymers were examined by the formation of soluble rGO/poly(ethylene glycol) (PEG) assembly, where PEG has the simplest structure among various water-soluble aliphatic polymers. Only high-molecular-weight PEG was successful for the formulation of soluble rGO/PEG assembly and therefore, van der Waals interaction (or sigma-pi interaction) between pi-rich rGO and alpha-rich PEG was proposed. The thermal property of the resulting rGO/PEG composite (or assembly) was changed dramatically compared to that of the pristine PEG, depending on the amount of rGO in the composite.