The crystal structure of the title compound, C(11)H(9)NO(4), consists of infinite one-dimensional polymeric chains due to inter-molecular O-H⋯O hydrogen bonds between the carboxyl-ate and carbonyl groups. The phthalimide ring system and the C-COO group are planar, with r.m.s. deviations of 0.0253 and 0.0067 Å, respectively, from their mean square planes and the dihedral angle between them is 66.41 (7)°. The mol-ecules are stabilized by C=O⋯π inter-actions and weak intra-molecular C-H⋯O hydrogen bonds.