The dimensional stability and moisture excluding efficiencies (MEEs) of wood after acetylation, butyrylation, and hexanoylation, were evaluated in this study. After three acylation treatments, an excellent antiswelling efficiency of modified wood specimens was obtained. All the equilibrium moisture contents of acylated wood at three relative humidities (RHs) (33% RH, 65% RH, and 93% RH) were significantly reduced, as compared to those of untreated wood in the same RH, and the MEEs of acylated wood were greatly improved. Acylated wood has consistent MEE at each of the different RHs. With the same percentage of substituted hydroxyl groups, the decreasing order of the MEE of modified wood was hexanoylation > butyrylation > acetylation. This indicates that the molecular volume or hydrophobic property of the substituted acyl groups also has the influence on the MEE of modified wood, in addition to the degree of substitution of the hydroxyl groups.