The title compound, C(11)H(12)ClNO(4)S, adopts a Z configuration about the C=C double bond. The benzisothia-zole system is essentially planar [maximum deviation of 0.235 (2) Å for the S atom]. In the crystal, the mol-ecules stack parallel to each other in the b-axis direction, with inter-planar spacings for the benzene and thia-zole rings ranging from 3.402 (2) to 3.702 (2) Å.