In the title compound, C(18)H(16)O(4), a monoprenylated xanthone, the xanthone skeleton exhibits an essentially planar conformation (r.m.s. deviation 0.0072 Å) and the isoprenyl side chain remains approximately in the mean plane of the xanthone unit, making a dihedral angle of 4.5 (2)°. The hydroxyl group forms an intra-molecular O-H⋯O hydrogen bond. Moreover, there is a weak inter-molecular C-H⋯O inter-action between a ring C atom and the xanthene O atom. In the crystal structure, there are no inter-molecular hydrogen bonds and the crystallographic packing is governed by van der Waals forces, leading to an arrangement in which the mol-ecules assemble with their planes parallel to each other, having a separation of 3.6 (3) Å.