A side-chain liquid crystalline polymer,poly{n-[(4'-hexylcarbonyl-biphenyl-4-oxy)]-1-propyne},is synthesized. It is a member of mono-substituted polyacetylenes. Its room temperature photoluminescence is investigated. At room temperature,its solution gives off intense deep-blue photoluminescence with its dominant emission band located at 380 nm. The 380 nm emission bands can be assigned to the emission from the isolated chain of the polymer. In order to confirm the origin of its photoluminescence,the electronic structures of the liquid crystalline polymer are calculated,and the absorption and photoluminescence are recorded from a small molecular liquid crystal that bears a biphenyl core.