Multi-walled carbon nanotubes (MWNTs) were modified by KOH in order to obtain high surface area with micropores. Pore characterization of modified MWNTs was performed with the observation of adsorption-desorption isotherms of N-2. According to the modification temperature of MWNTs increases, the specific surface area of MWNTs increases from 407 to 650 M-2 g(-1), on the other hand, the average pore width decreases from 2.77 to 2.13 nm. The isosteric heat value (q(st.phi-.1/e)) of modified MWNTs increased with the rise of modification temperature. The q(st.phi=1/e) of MWNTs increased in inverse proportion to the average pore width (w) and depended on the pore width. (c) 2005 Elsevier B.V. All rights reserved.