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CoO with porous nanowall structure is fabricated by a combined solvothermal and annealing process. The micromorphology of CoO is fine-tuned by controlling the annealing temperature. Nano-sized pores below ∼50 nm are achieved at 400 °C annealing with a high specific surface area of 65 m² g⁻¹. The unique porous nanowall structure leads to large surface areas and increase electrolyte/electrode interfaces, benefiting enhanced electrochemical performance of CoO. High specific capacitance of 352 F g⁻¹ has been obtained at 1 A g⁻¹ with good rate capability (72.7% capacitance retention from 1 to 20 A g⁻¹) and good cycling stability (92.9% of initial capacitance after 5000 cycles), making it a promising electrode for supercapacitor.