In this study, two novel 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine derivatives, 3-[2-(4-methoxyphenyl)ethyl]-6-phenyl-7H-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine (compound 1) and 3-[2-(3,4,5-trimethoxyphenyl)ethyl]-6-phenyl-7H-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine (compound 2), having analgesic-anti-inflammatory activity were synthesized and characterized by IR, (1)H-NMR, and mass spectroscopic techniques besides elementary analysis. Additionally, the structures and molecular packings of the mentioned compounds have been investigated by X-ray single crystal diffraction. The six-membered thiadiazine ring adopts the screw boat conformation in both the compounds. In the crystal packings of the compounds 1 and 2, C-H center dot center dot center dot N and C-H center dot center dot center dot O interactions link the molecules into a two-dimensional network and generate infinite chains. Furthermore, C-H center dot center dot center dot pi intermolecular interactions provide further stability to the molecular packing in both the molecules. The conformers have been predicted by the potential energy surface scan employing the AM1 method. Geometry optimizations and electrostatic properties have been obtained using AM1 and ab initio quantum methods.