In the mol-ecule of the title compound, C(15)H(11)NO(4), the essentially planar phthalide group is oriented at a dihedral angle of 56.78 (5)° with respect to the substituted aromatic ring. An intra-molecular N-H⋯O hydrogen bond results in the formation of a non-planar six-membered ring, which adopts a nearly flattened-boat conformation. In the crystal structure, inter-molecular C-H⋯O, O-H⋯O and N-H⋯O hydrogen bonds link the mol-ecules, generating centrosymmetric R(2) (2)(8) and R(2) (2)(11) ring motifs and forming a three-dimensional network.