From X-ray analysis, crystal and molecular structure of 4-acetyl-1,4-per-hydrothiazine-3-methylcarboxamide has been determined. Crystal data are as follow: orthorhombic, space group Pcab, a = 12.797(8), b = 9.923(7), c = 15.533(9) A, V= 1972.3 A*3, Z = 8.