Electrodes for electrochemical measurements have been fabricated using activated carbons (AC) prepared by waste medium density fiberboard containing 12% of urea-formaldehyde resin adhesive. The AC samples were activated by KOH at activation temperatures ranging from 700 to 900 °C (AC700–AC900) with an activation time of 60 minutes. As the elemental analysis show, the nitrogen content of all the AC samples decreased from 2.42% to 1.68% on increasing the activation temperature. The surface areas of the AC samples are in the range of 1308–1598 m² g⁻¹ with higher microspore volume between 0.5 and 2.0 nm. In addition, as shown by galvanostatic charge–discharge curves, cyclic voltammetry and alternating current impedance measurements, AC electrodes show superior capacitive performances. The electrochemical double layer capacitor was measured in a 7 M KOH electrolyte, which showed that the specific capacitances of AC700–AC900 varied from 176–232 F g⁻¹ under a current density of 50 mA g⁻¹. The AC800 exhibited the best electrochemical behavior with a specific gravimetric capacitance of 232 F g⁻¹ and rectangular cyclic voltammetry curves at a scan rate of 2 mV s⁻¹, which remained at 211 F g⁻¹ even at a current density of 10 A g⁻¹.