Polymerization of substituted acetylenes with the novel nickel catalyst system, Ni(COD)(2)-CF3COO(allyl), was examined. This catalyst system polymerized phenylacetylene to produce yellowish red polymers in good yield. The molecular weight of the poly(phenylacetylene) was 12,000. Disubstituted and aliphatic acetylenes hardly gave polymers by this catalyst system. The formed polymers had an alternating double bond structure. The UV-visible. spectrum of the poly(phenylacetylene) extended up to 550 nm.