Retropinacol rearrangement of serratenediol established that either terminal ring of this triterpenoid has the partial structure. The accumulated chemical and spectroscopic evidences have been summarized in the structure and stereochemistry containing seven-membered ring for serratenediol, which was confirmed by further degradation into a tricyclic ketone. The synthesis of this key product has now been achieved. The manner of acid isomerization of serratene derivatives has been also clarified. Serratenediol monoacetate, a minor triterpenoid constituent of Lycopodium serratum, was given a structure on ORD [optical rotatory dispersion] examination of various ketonic derivatives.