In this study, toughening of poly(lactic acid) (PLA) through reactive blending with epoxy-containing elastomer and ionomer was investigated. Four commercial ionomers based on the poly(ethylene-co-methacrylic acid) (EMAA) precursor were evaluated in this study, which contained zinc, magnesium, sodium, an lithium ions, respectively. Effects of metal ion type, elastomer/ionomer weight ratio and blending temperature on impact toughness of PLA ternary blends were studied. The toughening effects of metal ions of the ionomers is in the order of Zn > Mg > Li approximate to Na. High blending temperature and high elastomer/ionomer ratio both promoted the effective toughening of the PLA ternary blends. The reactive compatibilization and cross-linking of the epoxy-containing elastomer were analyzed using FT-IR, SEM, dynamic mechanical analysis, and torque rheology. In addition, the effect of metal ion type on thermal degradation of PLA was also examined.