Biomass-derived O/N-co-doped porous carbons have become the most competitive electrode materials for supercapacitors because of their renewability and sustainability. We herein present a simple approach to fabricate O/N-co-doped porous carbon nanosheets by the direct pyrolysis of Perilla frutescens (PF) leaves. Under optimum pyrolysis temperature (700 degrees C), the PF leaf-derived carbon nanosheets (PFC-700) having O, N contents of 18.76 at.% and 1.70 at.%, respectively, exhibit a hierarchical pore structure with a moderate BET surface area (655 m(2) g(-1)) and a relatively low pore volume (0.44 cm(3) g(-1)). Such O/N-co-doped porous carbon nanosheets display both high gravimetric capacitance (270 F g(-1) at 0.5 A g(-1)) and high volumetric capacitance (287 F cm(-3) at 0.5 A g(-1)). In addition, the PFC-700-based symmetric supercapacitor offers a high volumetric energy density (14.8 Wh L-1 at 490 W L-1) as well as a high stability (about 96.1% of capacitance retention after 10000 cycles at 2 A g(-1)). (C) 2016 Elsevier B.V. All rights reserved.