AbstractCarbon fibers (CFs) were mixed with wood fibers using the solution blend method to make highly conductive fiberboards. The microstructure, conductivity, shielding effectiveness (SE), and mechanical properties of fiberboards filled with CFs of various lengths and contents were investigated. The uniform distribution of CFs formed an excellent, three-dimensional conductive network. The CF-filled fiberboards exhibited evidence of percolation and piezoresistivity. A greater content of shorter CFs was necessary to realize the effects of percolation. The corresponding thresholds of fiberboards containing CFs of 2, 5, and 10 mm in length were 1.5%, 0.75%, and 0.5%, respectively. The volume resistance of fiberboards tended to be stable as the external pressure increased to 1.4 MPa. The volume resistivity of fiberboards reached equilibrium when the CF content was 10%. The fiberboards with greater than 10% CF content exhibited a SE of 30 dB above the average, yet they met the requirements for commercial application. The mechanical properties of fiberboards were investigated, and CFs were found to enhance the modulus of rupture (MOR) and modulus of elasticity (MOE). Therefore, it was concluded that fiberboards containing CF of 5 mm in length exhibited the best performance between percolation threshold and steady CF content.