An electrode-attached layer of poly(phenylacetylene) bearing a pendant nitronyl nitroxide group per repeating unit, obtained by the Rh-catalyzed polymerization of 2-(4-ethynylphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, underwent oxidation and reduction at 0.80 and 0.84 V vs. Ag/AgCl, respectively. The magnetically determined unpaired electron density of 92% was coulometrically reproduced, which supported the presumption that the radical survived during the course of the polymerization to allow both positive and negative charging of the pristine neutral polymer substantially per repeating unit. Galvanostatic Coulomb titration revealed the charge storage capability of the polymer, which demonstrated usefulness as organic electrode-active material with unprecedented ambipolar chargeability.