Carbon nanosheets (CNs) were successfully synthesized from nettle stem (NS) which is an inexpensive material with a high carbon content that is abundantly available in nature. CNs were produced using chemical (potassium hydroxide activation and acid exfoliation) and thermal treatments. Sulfuric (H2SO4), phosphoric (H3PO4) and nitric (HNO3) acid solutions were used for exfoliation. CNs exfoliated by H3PO4 have higher specific surface area (789 m2 g-1) compared to CNs exfoliated by H2SO4 (705 m2 g-1) and HNO3 (106 m2 g-1). In this work, NSCNs were found to be a potential candidate for electrode material in electrochemical capacitors. The maximum specific capacitance of the NSCNs exfoliated by H3PO4 is found to be 27.3 F g-1 at a current density of 0.05 A g-1, while the specific capacitance of NSCNs exfoliated by H2SO4 and HNO3 is 9.34 F g-1 and 1.71 F g-1, respectively. Energy density (0.06-0.95 Wh kg-1) and power density (20.9-26.7 W kg-1) of NSCNs are confirmed to be supercapacitor materials and can be applied in energy storage devices.