<p>Carboxymethyl cellulose ammonium salt (NH₄-CMC) is a unique water-soluble cellulose derivative that can be converted to water insoluble by heating due to NH₃ release. In this study, we propose a novel all-biomass composite sheet made by the wet extrusion of biomass powder using NH₄-CMC at room temperature. Paper or wood powder, NH₄-CMC, and water were blended, kneaded and extruded, then rolled up while drying to obtain all-biomass composite sheet. The tensile strength of the paper and wood powder sheet was equivalent to that of the paper. The sheets disintegrated readily in water as NH₄-CMC is water soluble, but did not swell or disintegrate after heating, especially to 150&#xa0;°C. The sheet absorbed moisture similar to paper and wood even after heat treatment owing to its all-biomass composite material. The tensile strength decreased with the increasing moisture content of the sheet. The paper powder sheet had higher tensile strength than the wood powder sheet because it has more cellulosic and easily binds strongly by a cellulose derivative. Most plastics in use today are derived from fossil resources and are non-biodegradable. Therefore, the development of an all-biomass material becomes imperative. This new extrusion process allows waste biomass powder to be effectively utilized and valorized into sheets, which could be a promising alternative to petroleum-based plastics.</p> Graphical Abstract <p></p>