Cellulose triacetate (CTA) was prepared from high-grade bamboo dissolving, pulp in general acetylation medium of acetic acid/acetic anhydride/sulfuric acid system. Despite its properties being improved compared with these of CTA prepared from viscose bamboo pulp, many insoluble residues still remained in its acetylation medium, which resulted in the decrease of the brightness and thermal stability of prepared CTA. Characterization of the insoluble residue indicated that its formation was associated with a higher content of xylan and ash in high-grade bamboo pulp than in high-grade hardwood pulp, in which insoluble residue was negligible. Because of the poor solubility of xylan diacetate (XDA) in acetylation medium, the insoluble residue formed through the aggregation of XDA and CTA by ultrastructural effects of the pulps during the precipitation of XDA. An addition to the good solvent of XDA, such as 1,2-dichloroethane to acetylation medium of high-grade bamboo pulp, could release the aggregation of XDA and CTA and dissolve the insoluble residue, which could lead to the improvement of the transmittance of reaction solution, is well as the properties of CTA prepared such as brightness and thermal stability. This study showed that high-quality CTA could be prepared from high-grade bamboo dissolving pulp in acetylation with an addition of solvent. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 456-465, 2009