In this paper, two nanoporous carbons were prepared from Sterculia lychnophora (SL) by simple hydrothermal conditions followed by a KOH activation step with and without a carbonization process. Structural characterization indicates that the carbon sample without the carbonization process (AC-1) exhibits a cross linked and hole-like structure, a BET surface area of 2589 m² g⁻¹, pore volume of 1.21 cm³ g⁻¹ and BJH average pore width of 2.78 nm. The carbon sample with the carbonization process (AC-2) shows dozens of nanometer microspheres, a BET surface area of 2660 m² g⁻¹, pore volume of 1.258 cm³ g⁻¹ and BJH average pore width of 3.321 nm. The electrochemical capacitance behaviors of these carbon materials were investigated in KOH and NaNO₃ aqueous solutions in three and two-electrode cells, respectively. By using the NaNO₃ electrolyte, the efficient capacitor can work in a wider voltage window of 1.7 V without any significant capacitance fading over 3000 cycles; the highest specific capacitance of 47.8 F g⁻¹ and energy density of 18.5 W h kg⁻¹ are demonstrated. The desirable porous structure and electrochemical characteristics may enable SL biomass based carbon to be excellent electrode materials for high performance electrical energy storage devices.