The title compound, C(16)H(20)O(5), was synthesized from ilicic acid [2-(8-hy-droxy-4a,8-dimethyl-deca-hydro-naphthalen-2-yl)acrylic acid], which was isolated from the chloro-form extract of the aerial part of Inula viscose (L) Aiton [or Dittrichia viscosa- (L) Greuter]. The molecule is built up from two fused six-membered rings, the epoxidized six-membered ring adopts a half-chair conformation while the other ring displays a perfect chair conformation. The crystal structure features C-H⋯O hydrogen bonds.