A series of highly functionalized quinazolin-4-ones, with different substituents at position 3, have been concisely synthesized in good yields, via the reactions of 3-amino-6-bromo-2-undecy-lquinazoline-4(3H)-one with one carbon donor isothiocyanatobenzene, followed by α-chlorinated compounds and 1,2-dichloroethanone. Moreover, reactions of 6-bromo-2-undecyl-4H-benzo-[3,1]oxazin-4-one with different hydrazides were also examined, giving new 3-substituted quinazolin-4-one derivatives. Some of the new quinazolin-4-ones were screened against gram negative and positive bacteria and showed good to moderate antibacterial activity. Structures of all new synthesized compounds in this investigation were substantiated using spectroscopic IR, 1H-NMR and MS studies.