Terahertz time-domain spectroscopy （THz-TDS） has been used to measure the vibrational spectra of polycrystalline D-, L- and DL-ornidazole over the temperature range 6—298 K. The large differences of the spectra are observed in the frequency range 0.3 THz—2.5 THz, which indicates that THz-TDS is an effective tool to distinguish between enantiomers （D-, L-ornidazole） and its racemic compound （DL-ornidazole）. A number of absorption peaks which could not be observed at room temperature are well resolved in the low temperature range. This provides more experimental details for mode assignment. The evolution of these absorption features between 6 K and 298 K was continuously mapped. The absorption frequencies shift to lower values as temperature increases. The measured temperature dependence can be well fitted if we consider the phonon modes follow a Bose-Einstein distribution. Finally, the quantum chemical calculations were carried out to simulate the experimental THz spectra of the three samples in the range of 0.2—2.5 THz. Compared with the calculated results, the observed characteristic absorptions are explained at molecular level.