Abstract: Micro/mesopore carbon spheres for use as the electrode materials of supercapacitors were prepared by hydrothermal carbonization followed by KOH/NaOH activation using sucrose as the carbon precursor. The effects of the KOH and NaOH activation parameters on the specific surface area, pore size distribution and electrochemical performance of the carbon spheres were investigated. Results indicate that the use of NaOH leads to the development of mesopores while the use of KOH increases the specific surface area and micropore volume. The pore size distribution of carbon spheres could be adjusted by varying the relative amounts of the reagents in the activation. Using a NaOH/KOH mass ratio of 2∶1 and a reagent/carbon sphere mass ratio of 3∶1, a good capacitance and rate performance of the supercapacitor electrode in both a 6 mol L⁻¹ KOH aqueous electrolyte and a 1 mol L⁻¹ MeEt₃NBF₄/propylene carbonate electrolyte was achieved. The prepared activated carbon gave a capacitance of 235 F g⁻¹ at 0.1 A g⁻¹ and a capacitance retention of 81.5% at 20 A g⁻¹ in the 6 mol L⁻¹ KOH aqueous electrolyte, and in a cell using the 1 mol L⁻¹ MeEt₃NBF₄/propylene carbonate electrolyte, it gave the highest energy density of 30.4 Wh kg⁻¹ and a power output of 18.5 kW kg⁻¹.