A series of some new 3, 5-diaryl-tetrahydro-N-formyl-1, 4-thiazine-1, 1-dioxides has been synthesized from their respective thiazine compounds. The structural assignments are based on their elemental and spectral data. All the synthesized compounds were preliminarily screened for their in vitro antimicrobial activity against Gram positive organisms (Bacillus subtilis, Staphylococcus aureus) and Gram negative organisms (Escherichia coli and Klebsiellapneumonia) and antifungal activity for Aspergillusnigerand Aspergillusfumigatus by disc diffusion method. Among the tested compounds, 8 showed the most potent antibacterial and antifungal activities.