A low-molecular-weight peptide(named Gt factor) was first isolated and purified from the extracellular culture of a brown-rot fungi Gloeophyllum trabeum. It could produce hydroxyl radical HO. in presence of O2 and Fe3+, might destroy hydrogen bonds of cellulose by HO.-involved oxidative mechanism, which was quite different from hydrolysis mechanism of cellulase in filamentous fungi. Gt factor might attack crystalline region of cellulose, bring about more reducing ends and non-reducing ends exposed, thus making cellulose accessible to further degradation.