High-pressure infrared (IR) absorption study of phase transition in pentaerythritol (PET) is reported. The changes in the IR spectra with increasing and decreasing pressure have been followed up to a maximum pressure of ≈11GPa. We observe several changes in the spectra including splitting of modes and sudden change in the slope of the frequency vs. pressure curve at about 4.7 GPa. The transition has been found to be completely reversible. We interpret these changes in terms of a symmetry lowering phase transition.