On the basis of the investigation on natural product antitumor agents,a new diterpenoid named macrocalyxin J was isolated from the leaves of Rabdosia macrocalyx（Dunn） Hara by silica gel column chromatography.Based on IR,MS,1H NMR,13C NMR and 2D NMR spectroscopies,the structure of macrocalyxin J was determined as（1α,6β,11β,14α）-1,7∶6,20-diepoxy-6,11-dihydroxy-6,7-seco-ent-kaur-16-ene-7,15-dione-14-acetate.The antitumor activity of the compound was assayed by MTT method.Macrocalyxin J was shown to have a potency in vitro against the cultures of Hela cells.
