There is provided a method of manufacturing hydrophilic carbon nanotubes, which is capable of imparting hydrophilicity without damaging the surface of the carbon nanotubes. By irradiating carbon nanotubes 4 with ultraviolet ray 3, hydrophilic functional group(s) are introduced into the surface of carbon nanotubes 4. Hydrophilicity is imparted to the carbon nanotubes to such an extent that a contact angle of water is in the range of less than 130.degree.. Ultraviolet ray 3 is a far ultraviolet ray having a wavelength ranging from 1 to 190 nm. The irradiation with ultraviolet ray 3 is conducted in the presence of oxygen and hydrogen or in the presence of ozone and hydrogen. The end part(s) of carbon nanotubes 4 is opened by the irradiation with ultraviolet ray 3.