Oleanolic and ursolic acids were used as lead compounds to synthesize a series of pentacyclic triterpenoid derivatives bearing ethylenediamine, butanediamine, or hexanediamine groups at the C-3 position. The potential antiproliferative activity of these compounds was examined in A549 (human non-small cell lung cancer cells), MCF-7 (human breast cancer cells), and HeLa (human cervical carcinoma cells) cells. Methyl 3β- O -[4-(2-aminoethylamino)-4-oxo-butyryl]olean-12-ene-28-oate (DABO-Me) was identified as a promising antiproliferative agent in vitro and in vivo . DABO-Me strongly suppressed the proliferation of A549, MCF-7, and HeLa cells (IC₅₀ = 4–7 µM). In MCF-7 cells, DABO-Me upregulated the pro-apoptotic protein Bax, downregulated the anti-apoptotic protein Bcl-2, promoted the release of cytochrome c , and activated caspase-3/9. Transwell and flow cytometry assays showed that DABO-Me inhibited MCF-7 cell proliferation, migration, and invasion, and induced apoptosis and S phase arrest. In vitro and in vivo experiments indicated that DABO-Me inhibited MCF-7 cell proliferation and suppressed tumor growth. Taken together, these results indicate that DABO-Me could be developed as an effective antitumor drug.