A novel optically active phenylacetylene derivative, N-(tert-butoxycarbonyl)-4-ethynyl-L-phenylalanine methyl ester (1), was synthesized from L-tyrosine and polymerized with a rhodium catalyst. The corresponding polymer [poly(l)] with a moderate molecular weight was obtained in a high yield. The alkaline hydrolysis of poly(l) gave poly[N-(tert-butoxycarbonyl)-4-ethynyl-L-phenylalanine] [poly(2)] carrying free carboxy groups. Polarimetric, CD, and UV-vis spectroscopy analyses revealed that poly(l) took a predominantly one-handed helical structure in MeOH and toluene, and poly(2) took a helical structure in MeOH. The secondary structures of poly(l) and poly(2) could be tuned with heat and solvents. (c) 2007 Wiley Periodicals, Inc.