This study investigated that epoxidized soybean oil(ESO) was blended as plasticizer with poly(lactic acid)(PLA) and its effects on the melt rheological properties,such as melt flow index,apparent shear viscosity,and melt strength of the blends.PLA was blended by the twin-screw plastic extruder at five mass fractions:3%,6%,9%,12%,and 15%(based on PLA mass).Melt flow index(MFI) was examined with a melt flow indexer.The results indicate that the blends of PLA/ESO had higher MFI than pure PLA,except for MFI at 9% reaching to the lowest point,even lower than that of pure PLA.Melt rheological properties were studied by a capillary rheometer in a temperature range of 160-180 ℃ .The blends exhibited shear-thinning behavior and the apparent shear viscosity was well described by the power law in this shear rate region.The melt strength of PLA plasticized with 6% ESO reached the maximums.ESO was more effective in increasing the melt strength at the mass fractions less than 6%,which could toughen the blends to some extent.Therefore,the authors suggested the optimum addition level of 6%-9% ESO will get good melt rheological performance balance. This study investigated that epoxidized soybean oil (ESO) was blended as plasticizer with poly (lactic acid) (PLA) and its effects on the melt rheological properties, such as melt flow index, apparent shear viscosity, and melt strength of the blends. PLA was blended by the twin-screw plastic extruder at five mass fractions: 3%, 6%, 9%, 12%, and 15% based on PLA mass. Melt flow index (MFI) was examined with a melt flow indexer. The results indicate that the blends of PLA / ESO had higher MFI than pure PLA, except for MFI at 9% reaching to the lowest point, even lower than that of pure PLA. Melt rheological properties were studied by a capillary rheometer in a temperature range of 160-180 ° C. The blends exhibits shear-thinning behavior and the apparent shear viscosity was well described by the power law in this shear rate region. The melt strength of PLA plasticized with 6% ESO reached the maximum. ESO was more effective in increasing the melt strength at the mass fractions less than 6%, which could toughe n the blends to some extent.Therefore, the authors suggested the optimum addition level of 6% -9% ESO will get good melt rheological performance balance.