Abstract The flower oil of Ridolfia segetum (L.) Moris of Tunisian origin was analyzed by GC and GC/MS. The main constituents of the oil were myristicin and dillapiole, the amounts of which varied depending upon the length of time the flowers were hydrodistilled. The contents of myristicin and dillapiole varied from 13.1â31.5% and 29.5â85.4%, respectively. Oil samples (fractions) were taken every 10 min from 10 to 150 min. Each fraction was screened against three Gram-positive and three Gram-negative bacteria. It was found that the antibacterial activity of the fractions was directly related to their proportions of monoterpenols and phenolic derivatives.