In the title compound, C(8)H(10)ClN(3)O(2)S, the oxadiazinane ring is in a sofa conformation with the ring O atom deviating from the best plane of the remaining five atoms by 0.636 (2) Å. A short intra-molecular C-S⋯O=C contact [S⋯O 3.122 (2) Å, C-S⋯O 80.0 (2)°] is observed between the two mol-ecular fragments bridged by the methyl-ene group. In the crystal, C-H⋯O hydrogen bonds link mol-ecules, forming chains along the b axis.