Abstract: Eight constituents were isolated from the leaves and stem of Rabdosia serra (Maxim) Hara, one of them is a new diterpenoid named rabdoserrin A (Ⅰ). Its structure was confirmed as ent-1,14-dihydroxy-7,20; 19,20-diepoxy(1a, 4a, 7a, 14R, 20R)-kaur-16-en-15-one by spectroscopic and chemical methods. Six known compounds were identified as excisanin A (Ⅲ), kamebakaurin (Ⅳ), 2α, 3β-dihydroxy-urs-12-en-28-oic acid (Ⅴ),β-sitosterol (Ⅵ), ursolic acid (Ⅶ) and β-sitosterolglucoside (Ⅷ), respectively. (Ⅰ), (Ⅲ) and (Ⅳ;) showed in vitro cytotoxicity against cultured Hela cells.