In the title compound, C8H9NO4, the hydrogen bonds between the oxime O atoms and the N and O atoms of the neighbouring asymmetric unit result in the dimerization of the molecules, with D...A distances of 2.774 (3) and 3.144 (3) Angstrom for O-H ... N and O-H ... O, respectively. The hydrogen-bridged centrosymmetric dimers are cross-linked via additional weaker intermolecular hydrogen bonds between the CH3 group and the other O atom of the dimer, forming a polymeric network. The D...A distance of this second-order interaction (C-H ... O) is 3.450 (2) Angstrom. Structure analysis indicates that the oxime is in an E configuration. The whole molecule is planar, with a maximum deviation from the least-squares plane of 0.104 (2) Angstrom.