Thermal stability and thermal degradation kinetics of nanocomposites play an important role in many applications. In this study, nanocomposites based on poly (lactic acid) (PLA)/graphene containing 0.5 and 1 wt% were prepared via solution method. Functionalized graphene were prepared by acid treatment followed by grafting PLA on their surfaces. The functionalized graphene was characterized using fourier transform infrared spectroscopy (FTIR), Raman, elemental analysis, Fourier transform infrared attenuated total reflection (FTIR-ATR), Dynamic mechanical thermal analysis (DMTA) and thermogravimetry analysis (TGA). The results revealed a successful functionalization reaction. The morphology of nanocomposites was investigated by scanning electron microscopy (SEM). Thermal kinetics of samples was studied using TGA in multiple heating rates (5, 10, 20 and 30 A degrees C/min). Flynn-Wall-Ozawa (FWO) and Vyazovkin (VYZ) methods were considered as isoconversional models. Although the assumptions of the applied models were different, there was a good agreement between the models and obtained activation energies.