When used as an industrial polymer, poly(vinyl alcohol) (PVA) has the disadvantage of low thermal decomposition temperature. Therefore, various studies are under way to overcome this drawback. PVA is thermally decomposed in a two-stage process, in which radicals are formed in the first stage, and subsequently the backbone chain of PVA is decomposed via a chain reaction. Poly(3,4-dihydroxy-Lphenylalanine) (pDA) synthesized by the self-polymerization of 3,4-dihydroxy-L-phenylalanine (DA) has radical scavenging ability. Therefore, the thermal stability of PVA was improved by the radical scavenging ability of pDA. The thermal decomposition behavior of poly(lactic acid) (PLA) was compared with that of PVA, to confirm that the thermal stability improvement was due to the radical scavenging reaction. In addition, the radical scavenging ability of pDA was confirmed by using antioxidant reagents DPPH and ABTS. The thermal decomposition behavior of the polymer was characterized by TGA and DTG, and the radical scavenging activity was analyzed by UV-Vis spectrometry. (C) 2017 Elsevier Ltd. All rights reserved.