Poly(L-lactide) (PLA) was melt-blended with four rubber components-ethylene-propylene copolymer, ethylene-acrylic rubber, acrylonitrile-butadiene rubber (NBR), and isoprene rubber (IR)-in an effort to toughen PLA. All the blend samples exhibited distinct phase seperation. Amorphous PLA constituted a topologically continuous matrix in which the rubber particles were dispersed. According to Izod impact testing, toughening was achieved only when PLA was blended with NBR, which showed the smallest particle size in its blend samples. In agreement with the morphological analysis, the value of the interfacial tension between the PLA phase and the NBR phase was the lowest, and this suggested that rubber with a high polarity was more suitable for toughening PLA. Under the tensile stress conditions for NBR and IR blend samples, these rubbers displayed no crosslinking and showed a high ability to induce plastic deformation before the break as well as high elongation properties; this suggested that the intrinsic mobility of the rubber was important for the dissipation of the breaking energy. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 558-566, 2009