Graft copolymerization of epsilon-caprolactone (CL) and lactic acid (LA) onto cellulose diacetate (CDA) at the residual hydroxyl positions was conducted to obtain thermoplastic CDA. The effects of the reaction temperature and time and the CL/LA molar ratio in the feed on the progress of the graft copolymerization were investigated. The molecular weight of CDA was increased by this graft copolymerization. The oxycaproyl and lactyl molar substitutions (MSCL and MSLA, respectively) in grafted CDA (g-CDA) were determined through H-1-NMR spectral analysis. These MS values were controllable by changing the reaction conditions adequately. The flow temperature and melt viscosity of g-CDA decreased with an increase in the total substitution of MSCL and MSLA, and transparent polymer sheets could be obtained from the resulting g-CDA by hot pressing at around 200degreesC without adding any plasticizer. The mechanical properties of the molded g-CDA samples varied widely, depending on the different combinations of the MSCL and MSLA values; the g-CDA sheets became elastic when the MSCL was larger than the MSLA, and their tensile strengths were enhanced as the MSLA was increased. It was thus found that CDA was successfully plasticized by this graft copolymerization.