Abstract: Microcrystalline cellulose was cyanoethylated by using acrylonitrile as etherifying agent. Effects of reaction time and reaction temperature on degree of substitution (DS) of the product were studied. It was indicated that DS of microcrystalline cellulose increases with prolonging of reaction time or increment of reaction temperature under 50℃. The peak of hydroxyl group of the cyanoethylated microcrystalline cellulose obviously became weaker and shaped cyano absorption peak was observed by FT-IR. It was concluded that part of hydrogens of hydroxyl group were substituted by cyanoethyls. X-Ray diffration pattern showed that the original crystal structure of microcrystalline cellulose was broken. With increase of DS of cyanoethylated microcrystalline cellulose, thermoplasticity increased before DS reach 1.43, then receded with increase of DS, as shown by X4 microscopic melting-point and Vicat softening-point measurements. It was concluded in this study that the rate constant of cyanoethylation of microcrystalline cellulose was ordered by 1.30,1.61,1.94 and 2.26 s-1 under reaction temperature of 30,35,40 and 45℃ respectively. Activation energy of cellulose cyanoethylation was 29.8 kJ/mol.