A new prenylated benzoic acid, arieianal [3,4-dihydroxy-5-(E,E, E-11'-formyl-3',7',15'-trimethylhexadeca-2',6',10', 14'-tetraenyl)benzoic acid, 1], has been isolated from the leaves of Piper arieianum and assigned this structure on the basis of its spectral data.