<p>Dynamic and isothermal thermogravimetric (TG) analyses of Japanese beech (a hardwood) and Japanese cedar (a softwood) along with their delignified and ball-milled samples were conducted to understand the thermal reactivities of hemicellulose and cellulose in wood cell wall. As a result, both delignification and ball milling tended to increase the thermal reactivities of hemicellulose and cellulose in cell wall, but the influences varied depending on two wood species. These treatments tended to affect the reactivities of cellulose in cedar and hemicellulose in beech more significantly. These results are discussed in terms of the different hemicellulose chemical structures (sugar type, uronic acid and acetyl content) and assembly of hemicelluloses and cellulose crystallites in cell wall.</p>