The optical properties and electronic structures of one mono-substituted polyacetylene and two di-substituted polyacetylenes have been investigated. Each of the substituted polyacetylenes bears a carbazole unit in the side chain. In spite of the differences in their molecular structures,the dilute solutions(～1 × 10^－6 M)of these substituted polyacetylenes exhibit the same absorptions and the same deep-blue emissions(～360 nm). Interestingly,the absorption and emission spectra of these substituted polyacetylenes are similar to those of the small molecule carbazole. As the concentration of the substituted polyacetylenes increases to about 1 × 10^－3 M,we have detected intense blue emissions at about 475 nm. Using Huckel tight binding programs,we have calculated the electronic structures of the carbazole-containing polyacetylenes. Our results indicate that the absorption,the deep-blue emission(～360 nm)and the intense blue emission(～475 nm)originate from the carbazole chromophores in the side chain.