Woody biomass is anticipated to be a resource for a decarbonized society, but the difficulty of isolating woody components is a significant challenge. Brown-rot fungi, a type of wood rotting fungi, decompose hemicellulose particularly efficiently. However, there are few reports on the hemicellulases from brown-rot fungi. An α-L-arabinofuranosidase belonging to glycoside hydrolase family 51 (GH51) from the brown-rot fungus Gloeophyllum trabeum (GtAbf51A) was cloned and characterized in the present study. Analyses of the phylogeny of GH51 enzymes in wood rotting fungi revealed the existence of two groups, intercellular and extracellular enzymes. After deglycosylation, the recombinant GtAbf51A produced by Pichia pastoris appeared on SDS-PAGE as approximately 71,777 daltons, which is the expected molecular weight based on the amino acid sequence of GtAbf51A. Maximum enzyme activity occurred between pH 2.2 and 4.0 and at 50 °C, while it was stable between pH 2.2 and 10.0 and up to 40 °C. Due to the presence of a signal peptide, GtAbf51A was thought to hydrolyze polysaccharide containing arabinose. However, the hydrolysis rate of arabinosyl linkages in polysaccharides was only 3-5 % for arabinoxylan and 18 % for arabinan. GtAbf51A, in contrast, efficiently hydrolyzed arabinoxylooligosaccharides, particularly O-α-L-arabinofuranosyl-(1→3)-O-β-D-xylopyranosyl-(1→4)-β-D-xylopyranose, which is the principal product of GH10 β-xylanase. These data suggest that GtAbf51A cooperates with other xylan-degrading enzymes, such as β-xylanase, to degrade xylan in nature.