Natural products derived from plants have been extensively developed as alternative medicines due to their relatively minimal side effects. Here we present the purification and characteristics of parasitic acid, a novel trinorditerpene from Dysoxylum parasiticum leaf extract, and investigate various bioactivities. The structure of this compound was elucidated using extensive spectroscopic techniques, including 1D and 2D NMR, and high-resolution mass spectrometry, which revealed a unique trinorditerpene skeleton featuring a 3-carboxyfuran moiety. The purified trinorditerpene exhibited cytotoxicity against MCF-7 (IC50 29.0 ± 0.8 μg/mL), antioxidant effects in the DPPH radical scavenging assay (IC50 10.91 ± 0.04 μg/mL), and inhibition of α-glucosidase enzyme (IC50 36 ± 1 μg/mL). Docking studies were also undertaken to explore the binding activities. This is the first report of a trinorditerpene-type diterpene from D. parasiticum with this unique combination of biological activities. © 2025 by the authors.