Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characteriied separately. Nanocornposites from cellulose nanofibers (CNF) in the xyloglucan (XG) biopolynier matrix are investigated at different hydration states Films of XG, CNF, and CNF/XG composites are subjected to detailed H-2 and C-13 NMR relaxation studies. Since the H-2 NMR. signal arises from heavy water and the C-13 signal from the polysaccharides, - molecular Water and polymer dynamics is for the first time investigated separately In the neat components, H-2 transverse relaxation (T-2), data are consistent. With water Clustering at the CNF fibril sulfaces, but bulk spread of moisture in XG. The-new method results in a description of water interaction with the nanoscale phases. At low hydration) water molecules at the CNF/XG interface exhibit higher water-mobility-than in neat CNF or XG, due to locally high Water concentration. At the same time, CNF-associated interphase segments of XG Slower NMR-dynamics that in teat XG.