Abstract Infrared spectroscopy can be used efficiently by polymer and rubber technologists for identification of polymer, polymer–blend ratio calculation, raw material evaluation, study of reaction mechanism, microstructure determination, etc. The present article represents a method to characterize nitrile rubber by Fourier-transformed infrared spectrophotometry (FTIR). The absorbance ratio of specific peaks of different grades of nitrile rubber was correlated with the acrylonitrile content measured by the Kjeldhal method. The acrylonitrile content of unknown acrylonitrile butadiene rubber (nitrile rubber, NBR) was calculated from a calibration graph.