This study investigates the use of natural polyphenol extracts as antioxidants to stabilize poly(lactic acid) (PLA), a biobased polymer. The polyphenols were extracted from vegetal waste using microwave-assisted extraction, and their antioxidant activities were evaluated. Five extracts—green tea residues, pomegranate peels, grape marc, bramble leaves, and yellow onion peels—were selected for further testing due to their high antioxidant capacities. These extracts were incorporated into PLA at 2 wt %, and their effects on PLA's thermal and photostability were assessed. The results showed that grape marc and pomegranate peel extracts significantly improved PLA's thermal stability during processing and thermo-oxidation. Additionally, these extracts effectively hindered the photo-oxidation of PLA, making them promising natural UV stabilizers. The study highlights the potential of using natural polyphenol extracts as biobased antioxidants to enhance the stability and sustainability of PLA.This study investigates the use of natural polyphenol extracts as antioxidants to stabilize poly(lactic acid) (PLA), a biobased polymer. The polyphenols were extracted from vegetal waste using microwave-assisted extraction, and their antioxidant activities were evaluated. Five extracts—green tea residues, pomegranate peels, grape marc, bramble leaves, and yellow onion peels—were selected for further testing due to their high antioxidant capacities. These extracts were incorporated into PLA at 2 wt %, and their effects on PLA's thermal and photostability were assessed. The results showed that grape marc and pomegranate peel extracts significantly improved PLA's thermal stability during processing and thermo-oxidation. Additionally, these extracts effectively hindered the photo-oxidation of PLA, making them promising natural UV stabilizers. The study highlights the potential of using natural polyphenol extracts as biobased antioxidants to enhance the stability and sustainability of PLA.