Communication: Polymerization of p-(dimethylsilyl)-phenylacetylene in toluene at 25 and 80 degreesC using RhI(PPh3)(3) as the catalyst afforded highly regio- and stereoregular poly(dimethylsilylene-1,4-phenylenevinylene)s (cis-3a and trans-3a) containing 98% cis- and 99% trans-vinylene moieties, respectively. Similarly, poly(butylmethylsilylene-1,4-phenylenevinylene)s (3b with 91% cis- and 95% trans-structures) and poly(diisopropylsilylene-1,4-phenylenevinylene) with 95% trans-structure were synthesized. All polymers were soluble in common organic solvents, The trans-type polymers showed red shifts and hyperchromic effects in the UV-visible spectrum. The onset temperature of weight loss (T-0) of cis-3a was much higher than that of trans-3a.