The mol-ecule of the title compound, C9H9N3O2S, is built up from fused five- and six-membered rings connected to methyl-sulfanyl and nitro groups, respectively. The mean plane through the fused ring system is inclined slightly relative to the plane passing through the nitro group [dihedral angle = 3.6 (2)°]. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds and π-π inter-actions between imidazole rings [inter-centroid distance = 3.667 (3) Å], forming a three-dimensional network.