The title compound [systematic name: 2-(4a,8-dimethyl-1,2,3,4,4a,5,6,8a-octahydronaphthalen-2-yl)acrylic acid anhydride], C30H42O3, is a new isocostic anhydride which was synthesized from the aerial part of Inula Viscosa (L) Aiton [or Dittrichia Viscosa (L) Greuter]. The molecule adopts an essentially linear shape with two terminal fused-rings bridged by the anhydride group. The external rings have the same conformation (half-chair) while each of the two inner rings has an almost ideal chair conformation. In the crystal, intermolecular C—H⋯O interactions link the molecules into a two-dimensional array in the bc plane.