Abstract <p>Lupeol is a natural pentacyclic triterpenoid with a wide range of biological activities. In view of its good biological activity base, to further enhance the anti-tumor activity, the researchers designed and synthesized 15 lupeol-3-indazole derivatives. All synthesized compounds were tested for their in vitro antiproliferative activity by MTT against the human lung cancer cell line (A549), human liver cancer cell line (HepG2), and human breast cancer cell line (MCF-7). Structure–activity relationship (SAR) analysis indicated that lupeol-4-[(5-bromo-1<i>H</i>-indazol-3-yl)methyl]piperazine-1-carboxylate exhibited the most potent antiproliferative activity against MCF-7 cells (IC₅₀ = 4.53 μM), which was 13.69-fold higher than that of parent lupeol (IC₅₀ = 61.89 μM). In vitro anticancer mechanisms reveal that lupeol-4-[(5-bromo-1<i>H</i>-indazol-3-yl)methyl]piperazine-1-carboxylate increased intracellular reactive oxygen species (ROS) levels, reduced mitochondrial membrane potential, and modulated the expression of apoptotic proteins in a dose-dependent manner, thereby inducing apoptosis in MCF-7 cells. Collectively, these findings demonstrated that the introduction of an indazole substituent at the C³ position of lupeol significantly enhanced the anticancer activity of the compound, thereby laying a theoretical foundation for the development of novel triterpenoid-based anticancer agents.</p>