We report the first infrared spectra of pure gaseous cyanobutadiyne between 400 and 4000cm −1 . A great care has been taken to obtain a pure sample so that, for the first time, intensities could be determined for all the main bands in the studied domain. The results are compared with available theoretical works. A sample containing a mixture of HC 5 N and DC 5 N was also studied in the same wavenumber range. The data obtained in this study should be very useful to identify those compounds by IR spectroscopy and will allow the quantification of cyanobutadyine in various environments.