The light emitting properties from solid films of a mono-substituted polyacetylene,poly{n-[(4＇-hexylcarbonyl-bipheny1-4-oxy)]-1-propyne},are investigated as temperature drops from 300 to 18 K. At room temperature,the solid films of the polymer give off intense green photoluminescence with its dominant emission band and two minor emission bands located at 510,440 and 380 nm,respectively. The 510 and 440 nm emission bands can be assigned to the primary and the secondary excimer emissions of the polymer while the 380 nm emission band can be assigned to the emission from the isolated chain of the polymer. When the temperature drops from 300 to 18 K,the primary excimer emission band is red shifted from 510 to 560 nm while the secondary excimer emission at 440 nm disappears gradually,leaving the emission from isolated chain of the polymer separated from its excimer emission bands. These temperature-introduced changes in the photoluminescence are explained in terms of the morphological changes in the polymer at low temperature.