The gas-phase infrared and Raman spectra of 1,4-cyclohexanedione have been measured at 225 and 300 degrees C, respectively. Geometry optimizations and vibrational ab initio calculations were carried out at the MP2/6-31G** level. It was found that the observed spectra are reproduced by assuming the coexistence of twist and chair conformers. Some vibrational bands in the infrared spectra showed splitting and temperature dependent intensities, indicating that the twist conformer has a lower enthalpy than that of the chair conformer.