A seco-apotirucallane-type triterpenoid, namely angustifolianin (<b>1</b>), along with three dammarane-type triterpenoids, (20<i>S</i>, 24<i>S</i>)-epoxy-dammarane-3β,25-diol (<b>2</b>), 3-epi-cabraleahydroxylactone (<b>3</b>), and cabralealactone (<b>4</b>), were isolated from the stem bark of <i>Aglaia angustifolia</i> Miq. The Chemical structure of the new compounds was elucidated on the basis of spectroscopic data. All of the compounds were evaluated for their cytotoxic effects against MCF-7 breast cancer cells. Among those compounds, angustifolianin (<b>1)</b> showed strongest cytotoxic activity with an IC₅₀ value of 50.5 μg/ml.

Keywords: Aglaia angustifolia; MCF-7; Meliaceae; angustifolianin; seco-apotirucallane.