The 1,3,4-oxadiazinan-2-one ring in the title compound, C(12)H(13)ClN(2)O(3), is in a distorted half-chair conformation. The phenyl and chloro-acetyl groups occupy axial and equatorial positions, respectively, and lie to the opposite side of the mol-ecule to the N-bound methyl substituent. Mol-ecules are consolidated in the crystal structure by C-H⋯O inter-actions.