In the title compound, C(8)H(7)ClN(4)S(2), the dihedral angle between the thia-zolidine ring (r.m.s. deviation = 0.028 Å) and the thia-zole ring (r.m.s. deviation = 0.004 Å) is 74.74 (6)°. The formonitrile group is almost coplanar with the attached ring [C-N-C-N torsion angle = 167 (2)°.