Some new 3-chloro-(4-substituted aryl)-1-(8-methoxy-[1,3,4]thiadiazino[6,5-b]indol-3-yl)azetidinones (4a-4g) have been synthesized from N-(substituted benzylidene)-8-methoxy-[1,3,4]thiadiazino[6,5-b]indol-3-amine (3a-3g). These newly synthesized compounds were characterized by elemental (C, H, N) and spectral (IR, 1HNMR mass) analysis. Compounds 3a-3g and compounds 4a-4g of the present series have screened for their antibacterial and antifungal activities. Compounds 4f and 4g were found to be the most potent members of the present series; they showed maximum antibacterial and antifungal properties much better than the standard drug. In this series Chloroamphenicol was used as standard drug for antibacterial activity and Fluconazole was used as standard drug for antifungal activity.