The grafted starch was prepared from corn starch and maleic anhydride. Fourier transform infrared spectroscopy (FTIR) was used to characterize the product. The Poly(lactic acid) (PLA)/grafted starch composites were prepared by means of a melt blending method. The effect of grafted starch content on the properties of the composites was investigated. The morphology of the composites was observed by scanning electron microscopy (SEM). Thermal degradation properties were studied by thermogravimetry (TG). The results indicated that the toughness could be improved obviously by adding suitable content of grafted starch. When 35 wt% grafted starch was added into PLA, the tensile strength decreased to 26.6 MPa from 51.7 MPa for pure PLA, elongation increased from 12.0% to 20.3%, flexural strength decreased from 99.0 MPa to 50.2 MPa, impact strength increased from 4.20 kJ/m2 to 6.28 kJ/m2.