Abstract: It has been known that' the mechanical preparation of wood surfaces or exposure of them to the ordinary atmosphere will induce free radical formation due to molecular fractures of wood chemical components. Thus, mechanical or photochemical actions may lead. to the modification of wood surface characteristics both chemically and physically. The present paper is dealing with some results of ESR investigation of free radical formation and decaying behaviors in the processes of wood cutting and photo-irradiations. Attempts are made to the identification of those free radicals and their reactivities with adhesives and the mechanism of photo-chemical reactions of wood are also discussed.