Some novel derivatives of quinazolinone including 2-[2-(2, 6-dichlorophenyl) amino]phenylmethyl-3-{4-[2( substituted phenyl)-4-oxo-thiazolidin-3-yl]phenylsulfonamido-1-yl}-6-bromoquinazolin-4(3H)ones (4a - 4l) were prepared from 2-[2-(2, 6-dichlorophenyl) amino]phenylmethyl-3-{[4-(N-substituted arylidene)phenyl]sulfonamide-1-yl}-6-bromo quinazolin-4(3H)ones (3a - 3l). Twenty four synthesized compounds were screened in vitro for their antibacterial and antifungal activities. Minimum inhibitory concentration (MIC) values of all the twenty four compounds were determined. Some of these compounds exhibited significant antimicrobial activity.