Disposable consumer electronics become electronic waste at the end of their life, which can cause serious environmental pollution if discarded in the ground. Here, we have developed an all-wood-based flexible electronic device. The substrate is used to prepare self-densification wood-derived paper (SWP) at room temperature through the natural balsa wood (NW) self-densification process. Chemical treatment removed lignin and hemicellulose from NW, and the cell wall structure collapsed under the action of elastic capillary force generated by water evaporation. The hydrogen bonds between the cellulose fibers are further strengthened, and the arrangement of the cellulose fibers is maintained. The obtained SWP exhibits an excellent tensile strength of 229.4 ± 10.4 MPa in the fiber direction, which is 8.3–8.6 times (27.1 ± 1.7 MPa) and 4.2–4.8 times (51.2 ± 5.6 MPa) higher than NW and cellulose paper, respectively, and higher than some commercial plastics. In addition, it also exhibits excellent wetting performance and a certain degree of transparency. Finally, conductive wood carbon ink prepared from carbonized NW can be directly written on SWP using a Chinese brush to obtain customized patterns. We have demonstrated the application of an all-wood-based flexible electronic device in flexible sensors that can stably monitor finger movements. This newly developed all-wood-based composite can return to the carbon cycle of nature after its service life, providing a new way to replace traditional electronic products.