Wood-based activated carbons were synthesized in a two-stage thermochemical process using sodium hydroxide as an activator, and used as the electrode materials for supercapacitors with a sulfuric acid electrolyte. The dependence of pore structure parameters and the electrochemical properties of the activated carbons on the synthesis conditions was investigated. Results indicate that an electric double layer is formed within micropores while meso and macropores are responsible for ion transport. Excess activation under a high activation temperature and/or a high mass ratio of sodium hydroxide to carbonaceous material leads to high meso and macropore volumes, which increase electrolyte uptake and therefore decrease the specific capacitance based on cell mass. The optimum activated carbon is obtained at an activation temperature of 600 °C with a mass ratio of sodium hydroxide to carbonaceous material of 1.25.