[en] Multi-walled carbon nano-tubes (CNTs) with a high specific surface area (SSA) present extensive applications in many fields. In this work, we investigate the nano-porous structures of CNTs activated by KOH under various temperatures of 700, 800, 850, and 900 C. A mild activation will generate a plenty of micro-structures and a strong activation will produce meso-pores. A highest specific surface area and a highest pore volume were obtained at a suitable temperature of 850 C. The temperature played an important effect on the activation process. It is suggested that the formation of nano-porous structure on the surface of CNTs may be related to appropriate potassium intercalation at a reasonable temperature. (authors)