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Poly(lactic acid)(PLA)is an important biodegradable polymer and is more and more expected as consumer products to substitute traditional oil-based materials.But brittleness,incompatibility and thermal instability afe critical defecfiveness for the manufacture of PLA.Poly(ethylene glycol)(PEG)and polycaprolactone(PCL)were both considered aS good blender for modification of PLA by many researchers.In order to compare these two blenders,PLA/PEG blends and PLA/PCL blends with variable ratios were prepared by twin screw extruder.For the higher market price of PEG and PCL,the weight percentage of PLA/PEG(or PCL)blends were 100％,0％.95％/5％,90％/10％,85％/15％and 80％,20％,respectively.The structural characterization of these two kinds of blend was elucidated using infrared adsorotion spectrum (IR)and proton nuclear magnetic resonance spectroscopy(1HNMR).And the thermal and mechanical propenies of these two kinds of blend were invegigated and compared by differential scanning calorimetry(DSC),tensile and impact tests,dynamic mechanical analysis(DMA)and scanning electron microscopy(SEM).The results indicated that even low ratios of PEG(or PCL),no more than 20wt％.can notably improve the thermal and mechanical properties of PLA.While there were still something difFerent between PLA/PEG blends and PLA/PCL blends in the effect of modification.PLA/PEG shows better compatibility than that of PLA/PCL,and the adding of PEG was much more effective on increasing elongation but sacririced much more modulus at the same time.whereas PCL iS less effective on increasing elongation but more effective on improving the impact resistance.meanwhile.with little loss of modulus.The intrinsic reason for this result indicated by DMA was that the remarkable elongation was mainly due to the stripping and plasticizing effect by crystallization of PEG whereas the elevated impact resistance essentially came from the good flexibility of PCL.