Temperature dependence of dielectric relaxation of 9-hydroxyphenalenone (1) is measured in the frequency region of 10(2)-10(7) Hz. We found a characteristic dielectric relaxation in the room temperature phase (phase II : 255-380 K), where the molecular orientation is known to be disordered. We ascribed the dielectric relaxation to the motion of boundaries between domains consisting of left- and right-directed molecules in the molecular chain.