The chemical compositions of hydrodistilled essential oils and n-hexane extracts from Origanum acutidens, O. rotundifolium and O. vulgare were analyzed by GC and GC-MS. Essential oils and hexane, chloroform, acetone and methanol extracts were tested against 25 plant pathogenic bacterial strains. Essential oils showed a wide spectrum of antibacterial activity, probably due to the phenolic components such as carvacrol and thymol. It was also shown that carvacrol, thymol and other main components such as terpinen-4-ol and linalool possess antimicrobial activity. Plant extracts, however, did not show any antibacterial activity, with the exception of the acetone and hexane extracts from O. rotundifolium. Our findings suggest that the essential oils may be valuable as potential antibacterial agents against plant pathogens, and show the potential value of Origanum oils as seed disinfectant.