Abstract: The carboxyl-terminated biodegradable polyester elastomer particles (CBEP)/poly (lactic acid) (PLA) composites were prepared by different particle sizes of CBEP blended with PLA. The mechanical, crystallization and degradation properties of the composites were tested, and the effect and mechanism of CBEP on the properties of PLA were studied.The results show that CBEP can significantly improve the toughness of PLA, and the composite specimens appear necking during stretching, especially the elongation at break of the composites with 7.5% (mass ratio to PLA) CBEP-a (particle size of 200 nm) increases from 4.6% of neat PLA to 155%. And the notched impact strength of CBEP/PLA composites is up to 2 times of neat PLA. CBEP can also improve the crystallization properties of PLA, in which the isothermal crystallization half-crystallization time of the composites with 7.5% CBEP-a (particle size of 200 nm) is shortened by 21.4% compared with the neat PLA.The results of the degradation experiments show that the mass loss of the composites with 10% CBEP-a (particle size of 200 nm) in lipase and soil environment is increased from 0.34% and 0.25% of neat PLA to 2.52% and 1.20%, respectively. The CBEP/PLA composites have broad development and application in the fields of biomedicine and environmentally friendly materials.