This study investigated the adhesion at the interface between mycelium and wood in detail, focusing on the evaluation of different bonding systems and the influence of hot-pressing temperature on bonding strength. The behavior of water-soluble components and their significance in this context were examined through chemical extraction experiments and analysis. The results indicated that both degraded wood veneer and surface mycelium exhibit comparable bonding strength. In addition, a significant finding of the study is that water-soluble components washed from mycelium, which exhibit a 7% higher protein content and a distinct carbohydrate composition compared to those washed from wood, are crucial in achieving effective bonding. Notably, proteins and high-molecular-weight carbohydrates are identified as key factors responsible for the favorable bonding behavior observed with mycelium. These findings offer valuable insights for the further development of sustainable materials utilizing mycelium as a binder and emphasize the importance of manipulating the composition of water-soluble components to optimize interfacial adhesion.