Abstract <p>We report a sustainable, wood-derived moisture energy harvester (WMEH) constructed from hierarchical cellulose micro/nanofiber films derived from wood residues, integrating bioinspired design, scalable manufacturing, and circular material principles. The device couples a hygroscopic LiCl-containing cellulose hydrogel with a conductive cellulose/carbon black/citric acid&#xa0;evaporative layer, establishing capillary-driven moisture transport and a&#xa0;sustained vertical humidity gradient. The hydrogel is constructed from cellulose micro–nano fibrils produced from wood residues, yielding hierarchically confined channels, electric double layer formation and ion-selective transport, and directional cation migration, enabling continuous moisture-to-electricity conversion in an asymmetric bilayer architecture. The WMEH delivers a high open-circuit voltage of 0.85&#xa0;V and a short-circuit current density up to 400 μA/cm², achieving a power density of 5.1&#xa0;μW/cm² and 164.5&#xa0;μW/cm³, competitive with state-of-the-art MEH. Continuous operation over 10&#xa0;days is maintained by a dynamic sorption-evaporation equilibrium, with stable performance across a wide humidity (20%–80% RH) and temperature (−20 °C to 50&#xa0;°C) range. Owing to intrinsic modularity, a 100-unit&#xa0;series and parallel assemblies deliver 74.5&#xa0;V and 1.46&#xa0;mA,&#xa0;respectively, sufficient to power commercial electronics without rectification. Beyond performance, the WMEH exhibits recyclability (about 95% voltage retention), biodegradability and substantially lower environmental impacts than representative carbon- and hydrogel-based moisture harvesters. This work highlights wood-derived cellulose micro/nanofiber films as a scalable fiber-material platform for sustainable moisture energy harvesting and decentralized power generation.</p> Graphical Abstract <p></p>