The poly(epsilon-caprolactone) (PCL)/starch blends were prepared with a coextruder by using the starch grafted PLLA copolymer (St-g-PLLA) as compatibilizers. The thermal, mechanical, thermo-mechanical, and morphological characterizations were performed to show the better performance of these blends compared with the virgin PCL/starch blend without the compatibilizer. Interfacial adhesion between PCL matrix and starch dispersion phases dominated by the compatibilizing effects of the St-g-PLLA copolymers was significantly improved. Mechanical and other physical properties were correlated with the compatibilizing effect of the St-g-PLLA copolymer. With the addition of starch acted as rigid filler, the Young's modulus of the PCL/starch blends with or without compatibilizer all increased, and the strength and elongation were decreased compared with pure PCL. Whereas when St-g-PLLA added into the blend, starch and PCL, the properties of the blends were improved markedly. The 50/50 composite of PCL/starch compatibilized by 10% St-g-PLLA gave a tensile strength of 16.6 MPa and Young's modulus of 996 MPa, respectively, vs. 8.0 MPa and 597 MPa, respectively, for the simple 50/50 blend of PCL/starch. At the same time, the storage modulus of compatibilized blends improved to 2940 MPa. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2724-2731, 2010