Different modifications of multiwalled carbon nanotubes (MWNTs) have been performed to increase specific capacitance of this material for supercapacitor application. MWNTs used in this work were obtained by decomposition of acetylene at 600 and 700 degreesC on cobalt catalyst supported on NaY zeolite, silica or produced from a CoxMg1-xO solid solution. Coming of MWNTs by conductin g polymers, e.g. polypyrrole (PPy) has been successfully realized and specific capacitance increased from ca. 50 to 180 F/g demonstrating a synergy between the two components of such nanocomposite. The open mesoporous network of well conducting nanotubular material allows an easy access of ions to the electrode/electrolyte interface and more effective contribution of the pseudofaradaic properties of PPy. Long durability (over 2000 cycles) was obtained for such supercapacitor material. The second way of MWNTs modification was their chemical activation by KOH. In this case, a significant enhancement of microporosity has been obtained and specific capacitance of nanotubular material increased from 15 to 90 F/g. (C) 2002 Elsevier Science B.V. All rights reserved.