The title compound, C(19)H(15)Cl(2)N(3)OS(2), was synthesized by the reaction of N-(2,4-dichloro-phen-yl)-5-(3,5-dimethyl-phen-yl)-1,3,4-thia-diazol-2-amine and mercaptoacetic acid. The thia-zolidinone ring adopts a twist conformation. The 2,4-dichloro-phenyl ring is almost perpendicular to the thia-diazole ring, the dihedral angle being 82.8 (2)°. The 3,5-dimethyl-phenyl ring is nearly coplanar with the thia-diazole ring, the dihedral angle being 2.7 (2)°. An intramolecular C-H⋯N hydrogen bond is present.