Possibility of living metathesis polymerization by Mo catalysts was examined for (p-n-butyl-o,o,m,m-tetrafluorophenyl)acetylene, which has two fluorine atoms at both ortho positions. The MoOCl4-n-Bu4Sn-EtOH (1:1:1) catalyst yielded a polymer with narrow molecular weight distribution ($$\left( {\bar M_{\text{w}} /\bar M_{\text{n}} = {\text{1}}{\text{.12}}} \right)$$), but the corresponding MoCl5-based catalyst did not formed such a polymer. With the former catalyst, the number-average molecular weight of polymer increased in direct proportion to monomer conversion, while the molecular weight distribution remained narrow; this proves the livingness of the polymerization. The optimal conditions for the living polymerization were [n-Bu4Sn]/[MoOCl4]=∼1.0, [EtOH]/[MoOCl4]=0.5–1.5, and temperature≤30 °C.n-Butyl acetate and acetone as well as EtOH were effective as third catalyst comp