AbstractGt factor, a pure component isolated from Gloeophyllum trabeum, was used to decompose lignin materials. The radical intermediates, degradation products and structural changes of treated materials were analyzed by infrared spectrum, NMR and electron paramagnetic resonance, etc. The results indicate that Gt factor makes an oxidative attack on lignin via HO˙, which might be the initial step in lignocellulose degradation by brown rot fungus.