Rubescensin D, a diterpenoid from Rabdosiarubescens. Eight flavonoids, 5,8,4′-trihydroxy-6,7,3′-trimethoxyflavone (1), 5,4′-dihydroxy-6,7,8,3′-tetramethoxyflavone (2), nodifloretin (3), pedalitin, (4), penduletin (5), cirsiliol (6), luteolin (7), and quercetin (8), were isolated from the aerial parts of Rabdosiarubescens A new diterpenoid of novel structure, rubescensin D, was isolated from Rabdosiarubescens and the structure determined by detailed spectroscopic analysis with emphasis on 2D NMR data, as well as chemical evidence. Apoptosis was up-regulated by Rabdosia rubescens, as seen in the caspase-9 and TUNEL assays. These effects may be mediated via both the MAPK (mitogen-activated protein kinase) and the Akt kinase pathways. In mouse experiments, the extract from Rabdosia rubescens suppressed breast cancer xenograft size and decreased the tumor vessel density.