NOVELTY - Modified carbon nanotube obtained by chemically bonding a polymer to a carbon nanotube by a radical graft reaction, is claimed. The polymer is synthesized by a living radical polymerization and has a living radical end group.    USE - The modified carbon nanotube is useful in a carbon nanotube electrode (claimed), which is useful as a counter electrode or transparent electrode for a dye-sensitized solar cell.    ADVANTAGE - The modified carbon nanotube has an excellent dispensability, catalytic characteristics, chemical stability, high electric conductivity and a longer life-span. The carbon nanotube electrode replaces indium tin oxide or fluorine-doped tin oxide substrate, which enables an expensive substrate having a transparent conductive film not to be required, resulting in low production costs and commercialization of dye-sensitized solar cells. The modified carbon nanotube electrode has a thinner film and more excellent photoelectric conversion efficiency than the conventional carbon nanotube electrode. The modified carbon nanotube film enhances adhesion strength between the substrate and the carbon nanotubes film and enhances the workability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a method for preparing a modified carbon nanotube, comprising: preparing a polymer synthesized by a living radical polymerization of an unsaturated monomer; and reacting the polymer with a carbon nanotube by a radical graft reaction, thus chemically bonding the polymer to the carbon nanotubes;    (2) a carbon nanotube electrode comprising: a substrate; a carbon nanotube film formed on the substrate; and the modified carbon nanotubes;    (3) a method for preparing a carbon nanotube electrode, comprising: preparing a dispersion liquid of the modified carbon nanotubes, which is dispersed in a solvent; and forming a carbon nanotube film by depositing the dispersion solution on a substrate; and    (4) a dye-sensitized solar cell, comprising: a semiconductor electrode; the carbon nanotube electrode; and an electrolyte filled between the two electrodes.