Abstract: In order to obtain poly(lactic acid) (PLA) matrix biodegradable blends whose stiffness is balanced with toughness, PLA/poly(butylenes adipate-co-terephthalate) (PBAT)/poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) fully biodegradable blends with different mass ratios were prepared by melting co-extrusion method. The morphology structures, thermal characteristics, rheological behavior and mechanical properties of PLA/PBAT/PHBV blends were investigated with SEM, TG, DSC, capillary rheometer and universal material testing machine. The results show that the initial decomposition temperature of PLA/PBAT/PHBV blends increases by 45 ℃ compared with pure PHBV, and the thermal stability of PLA/PBAT/PHBV blends is enhanced. Glass transition temperatures of each component in the blend system change little compared with the unitary system, which indicates that the PLA/PBAT/PHBV blend system is a complete incompatible system. At the same time, the cold crystallization of PLA is confined by the incorporation of PBAT and PHBV. The blend morphology of PLA/PBAT/PHBV blend system presents as a "sea-island" distribution, PBAT and PHBV distribute in PLA matrix evenly, and the interfaces between different phases are clear. When the content of PBAT increasing, the rheological of PLA/PBAT/PHBV blends melt is improved, and the effect of temperature on viscosity increases. The tensile strain of PLA/PBAT/PHBV blends with PLA/PBAT/PHBV mass ratio of 70/20/10 improves to 2.6 times of that of pure PLA, the toughness has been improved, and in the meanwhile, 60% tensile stress of pure PLA can be maintain. The conclusions obtained show that the comprehensive mechanical properties of PLA/PBAT/PHBV blends with PLA/PBAT/PHBV mass ratio of 70/20/10 is better than that of pure PLA.