Highly active Rh-based living polymerization catalysts were developed, which enabled the synthesis of poly( phenylacetylene) with high molecular weight and narrow molecular weight distributions (e.g., Mn) 195000, M-w/M-n = 1.06). For instance, a Rh-based ternary catalyst system composed of [(tfb)RhCl](2) (1) (tfb, tetrafluorobenzobarrelene), Ph2C=C(Ph)Li, and Ph3P (1:5:10) mediated the living polymerization of phenylacetylene (PA) with virtually 100% initiation efficiency. Furthermore, a well-defined vinylrhodium complex [(tfb)Rh-{-C(Ph=CPh2}(Ph3P)] (2) also polymerized PA in a living fashion with quantitative initiation efficiency in the presence of at least 5 equiv of Ph3P to Rh. The livingness of these polymerizations was confirmed by multistage polymerization, first-order linear plot, and effect of initial monomer concentration on molecular weight and MWD, and their initiation efficiencies were practically quantitative. A salient feature of catalyst 2 is its high activity even at a very low concentration ([M](0)/[Rh] = 4000, [Rh] = 0.125 mM) to quantitatively afford a high molecular weight polymer (Mn = 401000) having very narrow MWD (M-w/M-n = 1.12). The formed polymers possessed highly stereoregular cis-transoidal main chain (cis contents >= 99%).