Toughening of poly(lactic acid) (PLA) biopolymer by particles of acrylic based core-shell rubber (CSR) was conducted to observe the influences of the rubber contents on the properties of the modified PLA. A series of PLA specimens modified with the CSR by 0.1-10 wt% was prepared by twin screw extrusion and injection. Diminishing brittleness was reflected in the dramatic increment of both the impact strength by threefolds and the elongation at break by fifteenfolds when CSR was employed by 10 wt%. The toughening was also accompanied with a decrease in the tensile modulus and strength. At low loading, the added CSR by 0.5wt% also assisted crystallization of the PLA by slightly lowering the crystallization temperature, allowing decreased processing time and improving the degree of crystallinity of the generally difficult to crystallize PLA.