A novel polyisoprenyl benzophenone derivative named eugeniaphenone (1) was isolated from the stem bark of Garcinia eugeniaefolia Wall. Its structure was elucidated by spectroscopic methods, including 1D and 2D NMR techniques, and confirmed by single-crystal X-ray diffraction analysis. It is the first example in which an isoprenyl unit formed a cyclobutane-containing side chain in the polyisoprenyl benzophenone derivatives.