It has been reported that acetylation reduces the sorption of wood, thereby increasing the stability of the acoustic and dimensional properties of wood under conditions of changing humidity. Bamboos used for making a Korean traditional flute were acetylated and their dimensional properties were evaluated by measuring Weight Percent Gain and thickness swelling in water. Before acetylation bamboos were vacuum-dried to 3~6% at $50{sim}80^{circ}C$ without degradation. The optimum reaction temperature and time for bamboo acetylation were found to be $120^{circ}C$ and 8 hours, respectively.