The strong surface hydration layer of nonfoulingmaterials plays a key role in their resistance to nonspecific protein adsorption. Poly（ethylene glycol） （PEG） is an effective example of materials that can resist nonspecific protein adsorption and cell adhesion. Thus, the strong interaction between water molecules and PEG was investigated through each T2 component in water/PEG mixtures using multiexponential inversion of T2 relaxation time measured by the Carr−Purcell−Meiboom−Gill （CPMG） sequence of low-field nuclear magnetic resonance （LF-NMR）. Results show that about one water molecule is tightly bound with one ethylene glycol （EG） unit, and additional water molecules over 1:1 ratio mainly swell the PEG matrix and are not tightly bound with PEG. This result was also supported by the endothermic behavior of water/PEG mixtures measured by differential scanning calorimetry （DSC）. It is believed that the method developed could be also applied to investigate various interactions between macromolecules and other small molecules without using deuterium samples, which might open a novel route to quantitatively measure guest−host interactions in the future.