In order to increase their specific surface area (SSA) and modify their pore structures, carbon nanotubes (CNTs) prepared by catalytical pyrolysis and the graphitized CNTs (GNTs) were activated by KOH. The effects of the activation temperature and KOH/ CNTs ratio on SSA and porous structures of CNTs were investigated. With the increase of activation temperature, SSA and the pore volume increased. With the increase of the KOH/CNTs ratio, SSA and micropores increased, and reached a maximum for 7:1 of the KOH/CNTs ratio. From the data, the relatively optimal activation condition to produce the activated CNTs with high SSA were achieved, which is about 900 degrees C of the activation temperature and 7:1 of the KOH/CNTs ratio. SSA of CNTs activated at this condition is 360.1 m(2)/g, which is about 14 times larger than that of the non-activated CNTs. The activation effect of GNTs is much lower than that of CNTs, since GNTs have more regular crystal structure. (C) 2006 Elsevier Ltd. All rights reserved.