Solution ESR spectra of alkali-metal-doped corannulene monoanion, C20H10- have been observed from RT to 183 K. Eleven peaks have been observed from RT to 273 K. As the decrease of temperature, the 11 signals due to ten equivalent protons split into complicated ones. This behavior has been interpreted in terms of pseudorotation about the C-5v. Jahn-Teller crossing. The potential barriers between five equivalent C-s wells originating from the fifth-order anharmonic term have been estimated to be ca. 2.2 x 10(-3) eV.