An all-cellulose composite was prepared from conventional filter paper by converting a selective dissolved fiber surface into a matrix. The structure and mechanical, thermal, and optical properties of this composite were investigated using X-ray diffraction, a scanning electron microscope, an optical microscope, a tensile test, and dynamic viscoelastic analyses. After optimizing the immersion condition of the filter paper in a solvent, the fibers, with selectively dissolved surfaces, were unified by compression followed by drying. The tensile strength of the composite reached 211 MPa at 25 degrees C, isotropically. This value was comparable or even higher than those of conventional glass-fiber-mat-reinforced composites. The composites possessed a high storage modulus of more than 20 GPa at -150 degrees C, and a storage modulus of the GPa order was maintained up to around 250 degrees C. The good interface is considered to bring optical transparency to this composite. In addition, this composite is composed of sustainable resources and is biodegradable after service, which gives it advantages with regard to disposal, composting, and incineration.