Southern pine and aspen flakes were acetylated with acetic anhydride alone without cosolvent of catalyst by a simple dip procedure. The new procedure greatly shortens reaction time and simplifies chemical recovery. Acetylation weight gains of 15per thousand to 20per thousand can be achieved in 1 to 3 hours with southern pine flakes and in 2 to 4 hours with aspen flakes. Flakeboards made from acetylated southern pine or aspen flakes absorbed much less water, both in water-soaking tests and when subjected to humid air, and swelled at a lower rate and to a lower extent than did control boards. Hygroscopicity of the resulting flakeboards decreased with increased level of wood acetylation. The equilibrium moisture content (EMC) for flakeboards made from acetylated flakes was lower at each relative humidity tested than that of control boards.