Abstract: Three pairs of B-seco-ent-kaurene type diterpenoids were isolated from Rabdosia rugosa (Wall. )Hara collected from Tibet, and the structures of them were elucidated. They are diterpenoids rugosanin(Ⅰ ) and dihydrorugosanin (Ⅱ ), isodocarpin( Ⅲ ) and dihydroisodocarpin (Ⅳ ), carpala-sionin(Ⅴ) and dihydrocarpalasionin (Ⅵ). ( Ⅰ ), (Ⅲ) and (Ⅴ) were isolated, respectively, in the. form of mixtures with their corresponding dihydrocompounds ( Ⅱ ), (Ⅳ ) and ( Ⅵ ). The structure identification was based on the mixtures of each pair. Diterpenoid (Ⅱ ) is a new compound; ( Ⅰ ), (Ⅳ ) and ( Ⅵ) are for the first time found in nature, ( Ⅲ ) and ( Ⅴ ) are known compounds.

Key words: Rabdosia, B-seco-ent-kaurene, Rugosanin, Dihydrorugosanin, Isolation and identification