Acetyl tri-n-butyl citrate (ATBC) and poly(ethyleneglycol)s (PEGs) with different molecular weights (from 400 to 10000) were used in this study to plasticize poly(L-lactic acid) (PLA). The thermal and mechanical properties of the plasticized polymer are reported. Both ATBC and PEG are effective in lowering the glass transition (T-g) of PLA up to a given concentration, where the plasticizer reaches its solubility limit in the polymer (50 wt % in the case of ATBC; 15-30 wt %, depending on molecular weight, in the case of PEG). The range of applicability of PEGs as PLA plasticizers is given in terms of PEG molecular weight and concentration. The mechanical properties of plasticized PLA change with increasing plasticizer concentration. In all PLA/plasticizer systems investigated, when the blend T-g approaches room temperature, a stepwise change in the mechanical properties of the system is observed. The elongation at break drastically increases, whereas tensile strength and modulus decrease. This behavior occurs at a plasticizer concentration that depends on the T-g-depressing efficiency of the plasticizer. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1731-1738, 2003.