Polymerization of 1-methyl-1-(1-naphthyl)-2,3-benzosilacyclobut-2-ene as a monomer by n-butyllithium and diphenylmethylsilyllithium gave polymers with reasonably well controlled molecular weight. Polymers from the (+)-monomer by these organolithium compounds were optically active with similar optical rotations, but with rather low stereoregularity. Ring-opening reactions of the compound by n-butyllithium and diphenylmethylsilyllithium, and that by benzyllithium as a model propagation reaction, too was regiospecific. However, all of these ring-opening reactions of the (+)-monomer did not proceed stereoselectively as anticipated. Stereoselectivity of the ring-opening reaction to give dimer was low, which suggested that the ring-opening reaction in the propagation step was also low.