It is well-known fact that dimensional stability of wood is greatly enhanced by acetylation of wood. This dimensional stability results from bulking of the reacted acetate within the cell wall, which reduces further swelling when the modified woods come into contact with water or water vapor. The purpose of this research was to determine the water absorption and dimensional stability of the acetylated solid wood in liquid water and in humidity tests. Beech and red oak were acetylated. Moisture and water absorption of acetylated wood were quite dependent on weight percent gain(WPG). Antiswelling efficiency(ASE) was quite dependent on WPG, but was not dependent on species.