Abstract: Crystalline structure and thermal property of cellulose triacetate(CTA) and cellulose diacetate(CDA) were studied.After acetylation of cellulose,the allomorph of CTA changed and the crystallinity decreased;however,amorphism is dominant in CDA obtained by hydrolysis from CTA and spinning resulted in the reduction of crystallinity in CDA.TG analysis showed that thermal stability of CTA was better than that of CDA,and the existence of acetyl could enhance the thermal stability of cellulose acetate.DTA analysis indicated that the peaks of melting and decomposition overlapped in CTA;however,the melting peak appeared in a lower temperature and the interval between the peaks of melting and decomposition enlarged in CDA because of its imperfect crystallite;on the other hand,glass transition of CDA was more evident,and its T_g was higher than that of CTA.