Various amounts of surface-grafted silica (g-SiO(2)) and un-grafted (SiO(2)) nanoparticles were solution blended with a copolymer of l-lactide and epoxidized soybean oil (PLLA-ESO) or PLLA. Chemical reaction between the low molecular weight (LMW) PLLA and surface of silica nanoparticles is confirmed by FTIR and TGA analyses. The amount of grafted LMW PLLA investigated by thermal gravimetric analysis (TGA) was about 14.9%-28.2% in weight. g-SiO(2) nanoparticles can be easily dispersed into PLLA-ESO matrix to form a uniform PLLA-ESO/g-SiO(2) composite. Thermal properties of PLLA-ESO/g-SiO(2) and PLLA/g-SiO(2) nanocomposites were subsequently investigated by the differential scanning calorimeter measurements (DSC). DSC analyses indicated that g-SiO(2) nanoparticles can serve as a nucleating agent for the crystallization of PLLA-ESO in the composites, while the melting temperature (T (m)) and the glass transition temperature (T (g)) of PLLA-ESO/g-SiO(2) nanocomposites seemed to be independent of loading of g-SiO(2) particles. The DSC curves of PLLA/g-SiO(2) nanocomposite obviously showed double melting peaks, while that of PLLA-ESO/g-SiO(2) nanocomposites only a single melting peak. PLLA-ESO/g-SiO(2) composites exhibited a higher tensile strength and elongation than that of PLLA-ESO/SiO(2) composites.