This study characterizes the freeze/thaw behavior of large unilamellar DOPC vesicles in the presence of 0.5 or 4 M NaCl and 73 to 146 mM trehalose using Fourier transform infrared (FTIR) spectroscopy. Differences in lipid hydration between cooling and heating caused hysteresis in lipid phase change behavior and altered post-thaw lipid chain order. Lipids transitioned to a more ordered state during cooling. However, with heating, there was further conversion to a more ordered state at temperatures lower than the chain melting temperature. This conversion was more pronounced at higher concentrations of NaCl due to the formation of NaCl dihydrate crystals and the resulting changes in lipid hydration. Trehalose was shown to be capable of abrogating the severe dehydration effect at sufficiently high trehalose/NaCl concentrations by suppressing the formation of the NaCl dihydrate crystals. Moreover, trehalose enhanced recovery of prefreeze membrane structure.