Ailanthone is isolated from the bark of Ailanthus altissima (Mill.) Swingle (Simaroubaceae). The mechanism that underlies the activity of ailanthone on MCF-7 cells was investigated by MTT assay. Breast cancer MCF-7 cells were treated with 0.5, 1.0, 2.0, 4.0 and 8.0 µg/ml ailanthone for 24, 48 and 72