The effect of different methods of surface layer modification on the thermal stability of electroless metallized polylactide (PLA) was investigated. The modification of polylactide was carried out by chemical or plasma methods, using acidic KMnO4 or alcoholic NaOH solutions. The oxidation induction temperature (OIT) and thermogravimetric properties of the metallized samples were determined. The study showed that the surface layer of the modified PLA was only slightly changed when using KMnO4 solution, which did not significantly influence the thermal stability of the samples. On the other hand, alcoholic NaOH solution clearly etched the surface of the examined samples with consequent deterioration of their thermal stability.