The micellization of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer in aqueous solution in the absence and presence of salts was studied by Fourier transform infrared (FTIR) spectroscopy. The temperature-dependent changes of the C-O-C stretching vibration band were used to denote critical micellization temperatures (CMT). The CMT of Pluronic F127 in aqueous solution was modified significantly by the addition of salts as previously shown. The proportion of the anhydrous methyl groups was increased, while the proportion of the hydrated methyl groups was decreased during the micellization process. The dehydration of the Pluronic F127 ether backbone in the micellization process could also be inferred by the FTIR spectral data from a shift of the frequency of the C-O-C stretching band toward higher wavenumbers and broadening of the bandwidth of the C-O-C stretching band. The salt influence on the bandwidth is stronger than that on the wavenumber for the C-O-C stretching vibration. The microenvironmental difference between the PPO and PEO blocks of the copolymer is smaller in aqueous KBr solution than in other types of salt solutions. It was also found that part of the PEO segments of Pluronic F127 in aqueous salt solutions are in the crystalline state.