Abstract The temperature dependence of the ultraviolet absorption cross sections of 1,3-butadiene, from 160 to 240 nm, and butadiyne (diacetylene) from 160 to 260 nm have been measured, in the gas phase, for temperatures ranging from about 220 to 330 K. The absorption spectrum of 1,3-butadiene shows several sharp absorption features between 160 and 190 nm and strong diffuse bands between 190 and 220 nm. The absorption cross sections, at absorption peaks, increased significantly with decreasing temperature, particularly in the range 185 to 215 nm. At about 220 nm, a cross over point, the absorption cross section remained unchanged with temperature variations while at wavelengths greater than 220 nm the cross section values decreased with decreasing temperature. A sharp absorption feature at 186.6 nm shows the most pronounced relative temperature effect with an increase in the cross section from 42.55 × 10 −18 to 78.70 × 10 −18 cm 2 for a temperature change of 333 to 218 K. The spectrum for butadiyne consists of a very strong absorption at 164.6 nm with a cross section of4.40 × 10 −16 cm 2, at 295 K, followed by the complex absorption features between about 200 to 250 nm. The cross section values at absorption peaks determined at low temperatures are significantly higher than those at higher temperatures.