The electrochemical properties of individual multiwall carbon nanotubes (MWNTs) coated with an amorphous carbon layer are reported. MWNTs were etched at potentials more positive than 1.7 V vs. Ag/AgCl (3 M NaCl) in an aqueous 0.1 M KCl electrolyte solution. The logarithm of etching rate was proportional to the applied electrode potential, suggesting a kinetic etching mechanism. The estimated charge necessary to etch a MWNT was smaller than the total charge passed during etching, indicating that current was consumed for other parasitic reactions. Transmission electron microscopy (TEM) images of partially etched MWNTs indicate that etching begins at the distal end and proceeds preferentially along the longitudinal axis of the nanotube. The amorphous carbon layer was etched more readily than the graphitic core. TEM images of completely etched MWNTs showed that the pore at the distal end was still open, and that the tip of the MWNT was sharpened. These results indicate that electrochemical etching might be useful for controlling the shape and length of carbon nanotubes. (C) 2002 The Electrochemical Society.