The vibrational modes in Hg 1- x Cd x Te epitaxial films were investigated by means of far infrared transmission spectra at temperatures from 4 2 to 300K.The observations were put forward in the spectral range from 20cm -1 to 350cm -1 , emphasizing the wavenumber region at the low frequency side of the reststrahlen absorption band.A series of single phonon and two phonon modes, defects induced vibrational modes and impurities levels were observed.