This paper reports effects of acrylic core-shell rubber (CSR) on mechanical and rheological properties of poly(lactic acid) (PLA)/CSR blends. The CSR was synthesized via a seeded emulsion polymerization with poly(butyl acrylate) and poly(methyl methacrylate) as core and shell, respectively, and then introduced to PLA using a twin-screw extruder. Toughness of the blends characterized was increased by shear yielding due to micro-voiding formed by de-bonding of CSR. Their shear viscosity, storage, and loss modulus measured using rotational rheometer increased with CSR content. An analysis using Cox-Merz law confirmed that two curves coincided well with each other, while exhibiting shear-thinning behavior.