The mol-ecule of the title compound, C(14)H(11)N(3)O(5), assumes an E configuration with respect to the methyl-idene unit. An intra-molecular O-H⋯O hydrogen bond is present in the mol-ecule. The dihedral angle between the mean planes of the two benzene rings is 5.46 (15)°. The crystal structure is stabilized by inter-molecular O-H⋯O, O-H⋯N, and N-H⋯O hydrogen bonds.