A novel MoOCl4-based binary catalyst, MoOCl4-n-BuLi, induced the living polymerization of o-CF3-phenylacetylene. A catalyst composition of MoOCl4:n-BuLi = 1:1 and anisole as polymerization solvent were favorable. The polydispersity ratio of the polymer was as small as 1.02; the initiator efficiency was no more than 1.5-2.5%. The living nature was confirmed by both multistage polymerization and time dependence of the polymerization. Ethanol in catalytic amounts decelerated the polymerization but hardly affected its living nature. n-Alkyllithiums were generally useful as second catalyst components. The polymerization proceeded in a living manner in the temperature range 0-30 degrees C. o-Me3Si-phenylacetylene, o-i-Pr-phenylacetylene, and 1-chloro-1-octyne also polymerized in a living fashion; their polydispersity ratios were 1.03, 1.08, and 1.08, respectively.