In the title compound, C12H7N3OS, the five-membered 1,3-thia-zolidine ring is nearly planar [maximum deviation = 0.032 (2) Å] and makes a dihedral angle of 84.14 (9)° with the phenyl ring. In the crystal, mol-ecules are linked by C-H⋯N hydrogen bonds into infinite chains along [-101]. C-H⋯π inter-actions contribute to the arrangement of the mol-ecules into layers parallel to (101).