Activated carbon useful as polarizable electrode material for an electric double-layer capacitor can be obtained by mixing a carbonaceous material and an alkali metal hydroxide while maintaining a solid state, granulating the obtained mixture while maintaining its solid state, dehydrating the obtained granulated substance while maintaining its solid state, and subjecting the granulated dehydration product obtained in the dehydration step to an activation treatment. The preferred pressure of the granulation treatment in the granulation step is 0.01 to 300 Torr, and the preferred temperature of the granulation treatment is 90 to 140.degree. C. The preferred pressure of the dehydration treatment in the dehydration step is 0.01 to 10 Torr, and the preferred temperature of the dehydration treatment is 200 to 400.degree. C.