The title Schiff base compound, C15H15N3O3, crystallizes with two mol-ecules (A and B) in the asymmetric unit. Each mol-ecule adopts an E conformation around the C= N imine bond. The two mol-ecules have minor differences in their conformations. In mol-ecule A, the dihedral angle between the nitro group and its benzene ring is 2.1 (2)° and that between the two benzene rings is 0.88 (7)°, while the corresponding angles for mol-ecule B are 5.7 (1) and 2.45 (6)°, respectively. In each mol-ecule, there is an intra-molecular O-H⋯N hydrogen bond. In the crystal, inversion-related mol-ecules are linked via O-H⋯O hydrogen bonds forming A-A and B-B dimers. These dimers are linked via C-H⋯O hydrogen bonds involving the nitro O atoms, forming A-A-A and B-B-B slabs that lie parallel to one another and to (010).