Ovarian cancer, the most lethal form of gynecological cancer worldwide with a poor prognosis, is largely driven by an immunosuppressive tumor microenvironment. In this study, we investigated the anticancer effects of hydnocarpin, a natural flavonolignan derived from the flowers of Pueraria lobata, focusing on its effects on ovarian cancer and tumor-associated immune cells, including ovarian cancer-stimulated macrophages (MQs) and T cells. Hydnocarpin exhibited potent cytotoxicity against multiple ovarian cancer cell lines but only minimal toxicity against normal ovarian surface epithelial cells. Mechanistically, hydnocarpin triggered caspase-dependent apoptosis, as evidenced by the activation of caspase-9 and -3, with limited involvement of caspase-8, indicating the activation of the intrinsic apoptotic pathway. Experimental data implicated reactive oxygen species generation as a key mediator of hydnocarpin cytotoxicity, and reactive oxygen species inhibition significantly inhibited this cytotoxicity. In addition to its direct tumoricidal effects, hydnocarpin reprogrammed the tumor-associated immune cells, ovarian cancer-stimulated macrophages and T cells, by downregulating the levels of M2 MQ markers and pro-tumoral factors (matrix metalloproteinase-2/9, C–C motif chemokine ligand 5, transforming growth factor-β, and vascular endothelial growth factor) and enhancing MQ phagocytosis. Additionally, hydnocarpin promoted T-cell activation (interferon-γ and interleukin-2) and reduced the expression levels of immune evasion markers (CD80, CD86, and VISTA). Overall, this study demonstrated the dual anti-tumor effects of hydnocarpin on both ovarian cancer cells and immunosuppressive immune components in the tumor microenvironment, highlighting its potential as a novel therapeutic candidate for ovarian cancer.