The thermomechanical degradation and thermostabilization of poly(lactic acid) (PLA) have been studied using subsequent extrusion cycles under different temperature profiles. Primary and secondary antioxidants were used to avoid degradation process during extrusion. Melt flow index (MFI), size exclusion chromatography (SEC), and infrared spectroscopy (FTIR) analysis were used to evaluate the degradation and stabilization of PLA. The MFI and SEC analysis show that the main thermodegradation mechanism of PLA is governed by scission reactions. FTIR analysis confirmed the SEC results and showed that the synergetic effect between primary and secondary antioxidant is a suitable way to thermostabilize the PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40023.