In the title compound, C(20)H(16)O(5), the dihedral angle between the naphthalene ring system and the benzene ring is 67.43 (5)°. The bridging carbonyl C-C(=O)-C plane makes dihedral angles of 82.64 (6) and 41.79 (7)°, respectively, with the naphthalene ring system and the benzene ring. The dihedral angle between the carb-oxy O-C(=O)-C plane and the benzene ring is 36.38 (7)° and that between the bridging carbonyl C-C(=O)-C plane and the carb-oxy O-C(=O)-C plane is 51.88 (8)°. The crystal structure is stabilized by inter-molecular O-H⋯O and C-H⋯O hydrogen-bonding inter-actions. An intra-molecular C-H⋯O hydrogen bond occurs between a naphthalene H atom and the carbonyl O atom of the carb-oxy group.