An optically active (>98.2% ee) five-membered cyclic silicon compound, (S)-2-(l-naphthyl)-2-phenyl-5,5-dimethy-1-oxa-2,5-disilacyclopentane, was synthesized by intramolecular hydrosilylation of (1S)-1-(1-naphthyl)-1-phenyl-1-vinyl-3,3-dimethyl-3-hydro-1,3-disiloxane in good yield (as high as 74.3%). This cyclic compound could be easily polymerized by common nucleophilic initiators, such as PhLi, MeONa, and t-BuOK. The polymerization using the lithium initiator showed a very high regioselectivity in ring opening (head-to-tail content 98.7% at 0 degrees C) and consequently afforded an optically active and highly isotactic poly[{(1S)-1-(1-naphthyl)-1-phenyl-3,3-dimethyldisiloxane-1,3-diyl}-ethylene] ([alpha](25D) = -8.5 degrees, M-n = 20 800 (calculated from Si-29 NMR), M-w/M-n = 1.12 (by SEC)).