Infra-red spectra of 1,2,5-oxadiazole have been measured between 4000 and 400 cm −1 in the vapour, liquid, and solid phases. The Raman spectrum of the liquid with polarization measurements has also been obtained. A vibrational assignment of the fundamental frequencies has been made on the basis of the rotational envelope analysis of the infra-red vapour bands and of the polarization of the Raman lines.