Butylammonium hexafluorosilicate, (n-C 4 H 9 NH 3 ) 2 SiF 6 , crystallizes at room temperature in the trigonal system with a probable space group P321. A new structural phase transition was detected at low temperatures for this compound by means of differential scanning calorimetry (DSC) and the basic thermodynamic data for this transition were determined. The internal vibrational modes of (n-C 4 H 9 NH 3 ) 2 SiF 6 were studied at ambient temperature and as a function of the temperature, through the phase transition, by means of Raman spectroscopy. The observed phase transition is associated with the dynamics of the system and is of the order-disorder type.