The feasibility of the effective utilization of combustion ash from a woody biomass power plant as a novel filler added to adhesives used in plywood production is investigated. For this, plywood was prepared with glues containing combustion ashes having different properties, and the adhesion performance of the glues was examined in detail and compared with that of a glue containing calcium carbonate powder as the filler. Through optical microscopy observations and analyses of the adhesive layer in the plywood, the relationship between the properties of the glue, the structure of the adhesive layer, and the adhesion performance was unraveled. Results revealed that the glue containing woody biomass combustion ash without the unburned carbon component shows a better and more homogeneous adhesion performance than that containing calcium carbonate powder. The adhesion performance could be enhanced more uniformly by decreasing the particle size of the filler. The study also indicated that the difference in the adhesion performance according to the kind of filler is not due to the difference in the chemical structure of the adhesive layer, but because of the difference in the denseness of the adhesive layer dominated by the viscosity of the glue. Thus, this study confirms that woody biomass combustion ash could be practically utilized as a filler substitute of calcium carbonate powder in glues for manufacturing plywood. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.