PROBLEM TO BE SOLVED: To provide a method for reducing or preventing the proliferation of bacteria or fungi to materials based on lignocellulose material, especially wooden pieces or sawdust. SOLUTION: In the method, the lignocellulose material, such as the wooden pieces or the sawdust, is processed with a chemical agent containing a hydrocarbon chain, which is selected from mixed carboxylic anhydrides and is suitable for securing to graft a plurality of hydrocarbon chains onto the material by covalent bonding.