The effect of the alkyl side chain oil the chiroptical properties of optically active poly(4-(2-hydroxyalkoxyl)phenylacetylene) (poly(]) and poly(2)) and poly(4-(1-hydroxyalkyl)phenylacetylene) (poly(3), poly((S)-4), and poly((R)-4)) films was examined. Poly(1) film showed a reversible color change between yellow and red along with change of circular dichroism (CD) by exposure to solvent vapor and/or by heating, while red poly(2) that had a longer alkoxyl group was not color-changeable. Poly(3) poly(4) films showed the reversible inversion of the CD spectra, which was completed within several minutes, by exposure to organic solvent vapor and by heating. The CD inversion at lower temperature was observed for poly((S)-4) and poly((R)-4) with a longer alkyl chain. Lyotropic liquid crystalline poly((S)-4) and poly((R)4) exhibited the highly induced CD and helical fibril structures in the film by selecting the casting solvent, indicating the formation of a predominantly chiral organization.