Waste fiberboards were used to produce N, O co-doped carbon dots (CDs) by acid etching method. The graphene hydrogels decorated with N, O co-doped CDs (GCD) were synthesized via hydrothermalmethod and optimized through differentmass ratios. The optimal composite electrode exhibited a high specific capacitance of 335.1 F g(-1) at 1 A g(-1), and a good mechanical flexibility with about 90.6% capacitance retention after 500 bending/unbending cycles. Furthermore, the assembled flexible supercapacitor owned an ideal cycling stability of 83.4% after 10000 charge/discharge cycles at 5 A g(-1). Such results demonstrated that N, O co-doped CDs played an essential and unique role in composite graphene hydrogel for improving the electrochemical performance of the flexible supercapacitor. (C) 2018 The Electrochemical Society.