The polymerization of phenylacetylene induced by UV irradiation of W(CO)6in carbon tetrachloride provided in high yield a polymer, whose molecular weight reached about 80,000. The polymerization did not proceed without UV irradiation or in the absence of a halogen-donating agent such as carbon tetrachloride. On the other hand, the polymerization of 2-chloro-1-phenylacetylene was best effected by Mo(CO)6, and did not require any halogen-donating agent (polymer MW 400,000). Polymerization of other acetylene derivatives was also examined.