In the metabolism of a lignin substructure model; syringaresinol by wood-rot fungi (Coriolus versicolor), formation of a new type of acetal linkage was detected. The new acetal linkage was formed by the addition of a primary alcohol group of metabolites to the quinone methide of syringaresinol, and these reactions were catalyzed by the phenol oxidizing enzyme. This is a first evidence indicating the possibility that the acetal linkage was one of the intermonomer linkages in lignin or one of the linkages in lignin-carbohydrate complex in plant cell wall.