The molecular-level response of RDX to hydrostatic compression was examined in a diamond anvil cell using Raman spectroscopy. The pressure-induced alterations in spectral profiles of the C-N stretching mode (886 cm(-1)) were studied up to 8.3 GPa. At pressures near 4.4 GPa, several changes of the C-N stretching mode become immediately apparent in Raman spectrum, such as large frequency shifts, line broadening, mode splitting, and intensity changes, which are associated with the alpha-gamma phase transition and rearrangement between the RDX molecules. The high pressure Raman spectra changes of the C-N stretching mode are indicative of an alpha-gamma phase transition, and also suggest the lowering of molecular symmetry and crystal symmetry, which are expected to provide some insight into RDX molecular stability and decomposition.