The effect various biologically compatible low molecular weight plasticizers (containing ester groups and hydroxyl groups) on stress-strain properties (modulus of elasticity, tensile strength, ultimate elongation, etc.) and the biodegradability (in phosphate buffer solution and in the soil) of the biodegradable aliphatic polyester - poly (lactic acid) (PLA) was studied. Films cast from the solution in chloroform (CPLA) as well subsequently thermally treated films (TPLA) were examined. It has been found (DSC method) that CPLA is almost completely amorphous, while TPLA – highly crystalline. TPLA is less resistant and much more compliant: shows about three times smaller value of modulus and more than 30 times higher ultimate elongation. Plasticizing leads to considerable increase of deformability CPLA. Significant drop of elasticity modulus with growth of plasticizers content was observed. Plasticizers effectively reduce the value of stress maximum, increase the ultimate tensile elongation and decrease the strength of CPLA. The glycerol triacetate (TA) with more similar molecule structure to PLA turned out to be a most efficient plasticizer. A presence of plasticizers facilitates the degradation process of CPLA in the phosphate buffer solution and in soil, as well