In the title compound, C(10)H(7)NO(2)S, the dihedral angle between the benzimidazole and malonaldehyde group is 1.41 (2)°. An intra-molecular hydrogen bond is formed between the NH group and one of the adjacent carbonyl O atoms. In addition, the NH group forms an inter-molecular hydrogen bond to a symmetry equivalent of this carbonyl O atom, connecting the mol-ecules into centrosymmetric dimers. The structure also contains C-H⋯O inter-molecular inter-actions.