In this paper, the THz spectra of hydration of nylon-6 is first observed. The nylon-6 samples were hydrated by both H2O and D2O, and the spectra corresponding to bound water was observed by taking the difference between the hydrated and dehydrated samples. The spectral features of the hydrated water were resolved into three Gaussian functions. For the assignment of THz spectra, ab initio molecular dynamics (AIMD) and solid-state density functional theory (DFT) simulations were performed. Through the intensity change of the observed bands, the dynamics of adsorbed water molecules is discussed. Finally, the insight gained through the assignment of the low-frequency spectra provides a concise description for the rate of hydration and dehydration in these materials, highlighting the utility of THz spectroscopy for characterizing such phenomena.