This study shows that controlled PLA chain mobility in poly (lactic acid)/polyamide11 (PLA/PA11) blends can lead to high performance materials. The addition of an appropriate amount of polyethylene oxide (PEO) or polyethylene glycol (PEG) to a PLA/PA11 blend reduces the interfacial tension and increases the interfacial interactions due to an increase in the PLA chain mobility. The mechanical properties of (PLAPEO)/PA11 50/50 systems are highly dependent on the PEO composition and at an optimal PEO concentration show a remarkable improvement in the Izod impact strength with specimens demonstrating 17.5 times the impact strength of the neat PLA and 3 times that of neat PA11. Also, these same blends show exceptional ductility with an elongation at break of 275% as compared to 5% for the neat PLA and 6% for PLA/PA11 without added PEO. Analysis of the fracture surface of the tough blends after impact indicates controlled interfacial debonding/cavitation at the continuous PLA/PA11 interface which leads to extensive shear yielding in the surrounding matrices. An excellent correlation is found between the optimal PEO composition for high performance properties and PEO limited miscibility in the PLA phase. When PEO phase separates in the PLA it tends towards the PLA/PA11 interface and provides a locus of failure for interfacial debonding. PEG is not as effective as PEO and it has virtually no effect on the mechanical properties of the PLA/PA11 blend since it phase separates at lower concentrations, thus limiting its effect on PLA mobility and ultimately providing insufficient plastic deformation to the PLA matrix. These results indicate that controlled PLA chain mobility through the use of an optimal concentration of an appropriate plasticizer is a highly effective approach towards the development of high performance PLA/PA11 blends. (C) 2017 Elsevier Ltd. All rights reserved.