Acylation of hinoki wood (Chamaecyparis obtusa Sieb. et Zucc.) with specificgravity of 0.42 was made by mareic anhydride without catalist and solvent. Thereaction condition was 80- 160℃ for 2h in liquid phase. The mechanical properties ofthe acylated wood material were measured by flexural vibration method and theantiswelling efficiencies were also obtained. The lowering of the mechanical propertiesis inevitable due to the decreasing of the cohesive force of the wood substance by thereaction with maleic anhydride. However, the material has both practical dimensionalstability and sufficient hygroscopicity.