Systematically investigations of the plasticizing effects of triacetine (TAc) on crystallization, chain mobility, microstructure, and tensile properties of the Poly (lactic acid)/triacetine (PLA/TAc) blends are reported. A new transition hump was observed on the tan 6 curve of PLA(x)TAc(y) specimens at temperatures ranging from -80 to -20 degrees C. Thermal, wide angle X-ray diffraction (WAXD) and dynamic mechanical analysis properties of PLA and PLA(x)TAc(y) series specimens suggest that PLA and PLA(x)TAc(y) series specimens can hardly crystallize by cooling the melt in room temperature. However, significant recrystallization of alpha form PLA crystals was found during the annealing processes of PLA(x)TAc(y) series specimens. Some "less perfect" beta form PLA crystals were found as the TAc contents of PLA(x)TAc(y) specimens reach 30 wt %. Further morphological analysis show that the inherent brittle deformation behavior of the PLA specimen was successfully transformed into relatively ductile fracture behavior after blending sufficient but optimum amounts of TAc in PLA resins. Possible reasons accounting for this interesting recrystallization, thermal, microstructure and tensile properties of PLA(x)TAc(y) specimens are proposed. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2757-2763, 2009