The gamma (gamma) radiation effects on the thermal properties of Poly(L-Lactic acid) (PLLA), and three PLLA nanocomposites containing 1, 3 and 5% montmorillonite MK10 clay were investigated in different solvents such as tetrahydrofuran, chloroform and 1,4 dioxane. The polymers were irradiated by gamma radiation at low absorbed doses of 1, 5, and 10 kGy. The thermal properties and molecular weight of the unirradiated and irradiated PLLA and its nanocomposites were characterized by Thermogravimetry (TG) and Gel Permeation Chromatography (GPC), respectively. The TG curves showed that the thermal degradation of the unirradiated PLLA and its nanocomposites occurred in only one stage. The activation energies of thermal degradation (E) for irradiated and unirradiated PLLA and its nanocomposites were determined by the Flynn-Wall-Ozawa (FWO) method. The E values of the polymer irradiated with gamma radiation seem to be smaller than those of unirradiated sample due to polymer bond scission. In addition, the calculated G values of the polymer and nanocomposites showed that the polymer structure was less stable when exposed to radiation with increasing % MK10 content. (C) 2013 Elsevier Ltd. All rights reserved.