The emergence of mycelium-bonded biocomposites has been stimulated in the quest for sustainable development. These biocomposites exhibit enhanced mechanical properties through hot pressing, with mycelium playing a crucial role as both the adhesive and reinforcing material in this composite system. This study aims to investigate and compare the effectiveness of different mycelium films for veneer bonding, with a specific focus on the interface between the mycelia and the substrate. Two fungal species, Pycnoporus sanguineus and Trametes versicolor, were utilized to colonize poplar veneers for 14 days. Subsequently, a wood bonding interface was successfully established between the mycelium film and the decayed veneer surface. The results revealed that bonded veneers with the mycelium film of Pycnoporus sanguineus exhibited higher adhesion strength with 1.76 +/- 0.16 MPa. A series of analyses have revealed the occurrence of both mechanical and chemical bonds between mycelia and wood. The bonding interface between mycelium and wood was formed by a synergistic combination of mechanical interlocking, hydrogen bonding interaction, Schiff base reaction, and lignin repolymerization. This study provides valuable insights into the underlying mechanisms involved in the formation of interfacial bonding by fungal mycelia.