AIMS: Fusarium graminearum is a toxic fungus that affects food and feed crops. Piper sarmentosum extract (PSE) is a potential source of anti-mildew natural products for the food and feed industry due to its various pharmacological properties. In this study, we evaluated the antifungal activity and untargeted metabolomics analysis of PSE against F. graminearum. METHODS AND RESULTS: Antifungal activity was evaluated using the mycelium growth rate method. Untargeted metabolomics analysis of PSE was performed using ultra high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that PSE (1 and 2 mg ml-1) possesses inhibitory activity against F. graminearum, and a total of 17 compounds that including 8 alkaloids, 3 phenols, 3 lipids, and 3 organic acids might be the antifungal markers in PSE. Metabolomics analysis further revealed that PSE could significantly increase the levels of guanosine, guanine, adenosine, and L-isoleucine in fungi, which are related to purine and L-isoleucine metabolic pathways. CONCLUSIONS: PSE is a promising anti-mildew agent that inhibits the growth of F. graminearum in food and feed. PSE (1 and 2 mg ml-1) may exert antifungal properties by inhibiting fungal purine nucleotide synthesis and enhancing the level of L-isoleucine compared with the control groups. CI - (c) The Author(s) 2023. Published by Oxford University Press on behalf of Applied Microbiology International.