An efficient approach to quinazolin-4(3H)-ones was developed by a one-pot intermolecular annulation reaction of o-amino benzamides and thiols. This method has the features of good functional group tolerance, being transition metal and external oxidant free, and easy operation. Varieties of 2-aryl (heteroaryl) quinazolin-4(3H)-one, 2-phenyl-pyrido[2,3-d]pyrimidin-4(3H)-one and 3-phenyl-2H-1,2,4-benzo thiadiazine-1,1-dioxide derivatives were obtained with a yield of up to 98%. The control experiment revealed that the thiol substrate could promote the dehydroaromatization step.