Simultaneous manipulation of topological and chemical structures to induce ionic nanochannel formation within solid electrolytes is a crucial but challenging task for the rational design of high-performance electrochemical devices including proton exchange membrane fuel cell. Herein, a novel generic approach is presented for the construction of tunable ion-conducting nanochannels via direct assembly of graphene oxide (GO)/poly(phosphonic acid) core-shell nanosheets prepared by surface-initiated precipitation polymerization. Using this simple and rapid approach to engineer GO/polymer nanosheets at the molecular-level, ordered and continuous nanochannels with interconnected hydrogen-bonded networks having a favorable water environment can be created. The resulting membranes exhibit proton conductivities up to 32 mS cm(-1) at 51% relative humidity, surpassing state-of-the-art Nafion membrane and all previously reported GO-based materials.