The title compound, C(20)H(30)O(6), a natural ent-kaurane diterpenoid, named nervosanin B, was obtained from the medicinal plant Isodon serra. It is composed of four rings with the expected trans and cis junctions. One of the six-membered rings is in a chair conformation, the other two are in boat conformations and the five-membered ring adopts an evenlope conformation. The mol-ecules stack along the a axis and are linked together by inter-molecular O-H⋯O hydrogen bonds. Two intramolecular O-H⋯O interactions also occur.