In this study, poly (lactic acid) (PLA) blended with various rubber components, i.e., poly (ethylene-glycidyl methacrylate) (EGMA), maleic anhydride grafted poly(styrene-ethylene/butylene-styrene) triblock elastomer (m-SEBS), and poly(ethylene-co-octene) (EOR), was investigated. It was observed that EGMA is highly compatible due to its reaction with PLA. m-SEBS is less compatible with PLA and EOR is incompatible with PLA. Electron microscopy (SEM and TEM) revealed that a fine co-continuous microlayer structure is formed in the injection-molded PLA/EGMA blends. This leads to polymer blends with high toughness and very low linear thermal expansion both in the flow direction and in the transverse direction. The microlayer thickness of rubber in PLA blends was found to play key roles in reducing the linear thermal expansion and achieving high toughness of the blends. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013