By melt blending of ESO with PLA and MCC, ternary composites with superior toughness are successfully manufactured. ESO is proved to be accumulated on the surface of MCC particle, which is mainly induced by chemical effect. Results reveal that the forma- tion of a thin ESO layer on MCC particles surfaces provides the ter- nary composite with the high interfacial adhesion and high deformation region to absorb large amount of energy in tensile process. With the increase in DS of MA, more ESO is accumulated on the surface on MCC to produce the highest toughness properties. The elongation and impact strength are finally improved up to 38.5% and 31.7 KJ/m2.