Cellulose is one of abundant resource on earth and referred to as“Biomass.”It is biodegradable and renewable resource of the future because petroleum-based plastics can be replaced by cellulose. However, neat cellulose has not good reactivity because of strong hydrogen bond. In this study, to make better reactivity of cellulose, cellulose was pretreated such as sonication and water activation. Neat cellulose was dissolved in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) system. Fatty acid and acetic anhydride was used to prepare cellulose mixed ester. Reaction was run in 8 h at 120℃. Pretreated cellulose was studied using Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) and thermogravimetric analysis (TGA). The results showed improvement of synthesis efficiency through morphology, structure and thermal properties of pretreated cellulose.