The family Lamiaceae is represented by 45 genera, 546 species and 730 taxa in Turkey. The genus Origanum is represented in Turkey by 22 species; the ratio of endemism in the genus is 63%. Origanum vulgare subsp. hirtum collected from different localities in Marmara region and their cultivated forms provided by the Atatürk Central Horticultural Research Institute Yalova/Turkey were subjected to hydrodistillation to yield essential oils which were subsequently analysed by GC and GC-MS. The main constituents of the oils were identified and antimicrobial bioassays were applied. The analyses showed that wild and cultivated Origanum vulgare subsp. hirtum oils contained carvacrol (82.9-7.5% and 85.4-5.3%, respectively) and thymol (60.1-0.3% and 68.0-0.3%, respectively) as the main components. The essential oils showed strong antimicrobial activity against all the microorganisms tested.