The purpose of this study is to monitor phase transformations in intact trehalose tablets using FT-Raman spectroscopy. Tablets of trehalose dihydrate, amorphous trehalose (obtained by freeze-drying aqueous trehalose solutions), and anhydrous trehalose (beta-trehalose) were prepared. The tablets were exposed to different conditions [11% and 0% RH (60 degrees C); 75% RH (25 degrees C)] and monitored periodically over 96 h using Raman spectroscopy. Within 96 h of storage, the following phase transformations were observed: (1) trehalose dihydrate-->beta-trehalose (11% RH, 60 degrees C), (2) trehalose dihydrate-->alpha-trehalose (0% RH, 60 degrees C), (3) beta-trehalose-->trehalose dihydrate (75% RH, 25 degrees C), and (4) amorphous trehalose-->trehalose dihydrate (75% RH, 25 degrees C). FT-Raman spectroscopy was a useful technique to identify the solid form and monitor multiple-phase transformations in intact trehalose tablets stored at different conditions.