The crystal structures are reported of the isomeric compounds 2-(4-nitrophenyl)-3-phenyl-2,3-dihydro-4H-1,3-benzothiazin-4-one, (I), and 2-(2-nitrophenyl)-3-phenyl-2,3-dihydro-4H-1,3-benzothiazin-4-one, (II), both C20H14N2O3S, being the para-nitro and ortho-nitro forms, respectively, the meta-form of which is known Yennawar et al. (2013). Acta Cryst. E69, o1679. The six-membered thiazone ring fused with a benzene ring displays a screw-boat conformation with a total puckering amplitude of 0.627 (1) Å in (I), and a near screw-boat conformation with a total puckering amplitude of 0.600 (1) Å in (II). The dihedral angles between the planes of the substituent nitrophenyl and phenyl and rings with the benzene ring of the parent benzothiazone moiety are 75.93 (5) and 82.61 (5)° in (I), and 76.79 (6) and 71.66 (6)° in (II). Weak intermolecular C—H...O hydrogen-bonding interactions between aromatic H-atom donors and both a nitro-O atom and a thiazone O-atom acceptor in (I) and a thiazone O atom in (II) are present, forming in (I) a centrosymmetric 22-membered cyclic dimer which is extended through a similar inversion-related 14-membered cyclic hydrogen-bonding association into a zigzag chain structure extending along c. In (II), a single intermolecular C—H...O hydrogen bond gives a chain structure extending along b. In addition, weak C—H...π interactions are present in both structures minimum C...ring-centroid separations = 3.630 (2) and 3.581 (2) Å, respectively.