This experiment was carried out to evaluate the role of oxalic acid metabolism in the incipient decay of brown rotting, and to investigate the effects of various compositions of culture medium. Until 5days incubation, the amount of oxalic acid produced by Tyromyces palustris was increased, while pH was gradually decreased. The difference in oxalic acid production depending on carbon sources was not significant and the pH adjustment of media did not stimulate the production of oxalic acid. In this experiment, hemicellulose was hydrolyzed with 1% oxalic acid, so it is suggested that nonenzymatic acid hydrolysis of hemicelluloses might be involved in the process of incipient decay of brown-rot fungi.