A simple, cost-effective, and environmentally friendly route was developed to synthesize graphene nanosheets from humic acid via preliminary carbonization coupled with oxidation-exfoliation-thermal reduction. Such graphene nanosheets have a high specific surface area (495 m(2).g(-1)) with large pore volume (2.987 cm(3).g(-1)), unique interconnected mesoporous structure and uniform oxygen-containing functional groups in layered graphene framework, which offer a favorable and efficient pathway for the electrolyte propagation and transportation. The electrodes of supercapacitors made from these graphene nanosheets exhibit a maximum specific capacitance of 272 F.g(-1) at the current density of 50 mA.g(-1) in aqueous electrolyte, and possess excellent rate capability, low resistance, superior cycling performance with over 96.5% initial capacitance retention after 8000 cycles. The corresponding supercapacitors deliver a desirable energy density of 6.47 Wh.kg(-1) at a powder density of 2250 W.kg(-1). This study demonstrates a promising synthesis route for large-scale production of graphene nanosheets from renewable and green humic acid for high performance supercapacitors. (C) 2017 Published by Elsevier B.V.