(CH3)2NH2NO3 belongs to the monoclinic space group P21/m with Z = 2 at 295 K. Raman and infrared spectra (10-5000 cm-1) of (CH3)2NH2NO3 and of its ND2 deuterated derivative were investigated in the temperature range 90-350 K. A systematic temperature dependent study of the frequencies and band widths showed the existence of a phase transition at 297 K. Assignments of most of the bands observed are proposed. The spectral features indicate that the high temperature phase I is disordered in which both cations and anions exhibit reorientational motion and the transition to phase II is brought about by freezing out the disorder of both the cations and anions. A soft mode has been identified in the low temperature phase. © 1988.