The size of fine structures in the quiescent prominence that appeared on August 16, 1992 has been estimated using power spectra generated from intensity variations of Ha images of the lower part of the prominence, which were taken with a G1 CCD camera attached to 25cm coronagraph at Norikura Coronal Station in Japan. The lower part of the prominence has shown a distinct intensity variation with optical thickness of $ au=1~5$. Our analysis yields a mean size of fine structures ranging from 350 km to 1,000 km, in good agreement with Hirayama(1985) and Zirker & Koutchmy(1989, 1991).