In a previous work [Macromolecules 2004, 37,1386], a new way of processing cellulose whisker reinforced nanocomposites from an organic solvent (N,N-dimethylformamide) without a surfactant addition or a chemical surface modification was investigated. This technique is used to prepare nanocomposite polymer electrolytes based on a cross-linked polyether and lithium imide (LiTFSI) reinforced with tunicin whiskers. Both the mechanical and ionic conductive properties of the resulting electrolytes are presented. These performances are compared to those obtained for unfilled cross-linked polyether matrices exhibiting several cross-linking densities. It is observed that the ionic conduction of cellulose whisker filled electrolytes is higher than the one of highly cross-linked polyether networks. In addition, the mechanical stiffness of the former is much higher than that of the latter, allowing the processing of high-performance nanocomposite polymer electrolytes.