The temperature dependence of the Raman and infrared spectra of solid 1,4,7-trithiacyclononane (TTCN) has been studied from 10 K to the melting point (355 K). Raman and infrared spectra of the liquid have been recorded from the melting point to 390 K. Differences between the spectra of the compound in the liquid and solid states indicate that there is a change from the conformation of symmetry D 3 in the liquid phase to one of C 3 symmetry in the solid. As the temperature is lowered from room temperature to 10 K, splitting of many bands in the Raman and infrared spectra is observed. This indicates that a further lowering of symmetry occurs at low temperatures. Anomalies in the solid-state frequency versus temperature plots have been observed for several internal modes. It is suggested that a structural phase change occurs in the crystalline solid near 225 K. Possible structures of the low temperature phase are discussed.