Volatile oils of Origanum vulgare L. in Shandong were separated by using microwave-assisted hydrodistillation (MHD 300 W, solid-to-liquid ratio 1∶10, microwave hydrodistillation time 1 h) and hydrodistillation (HD). The chemical components of the oils were identified by GC/MS technique and comparison of retention indices. Forty-two components were characterized, representing 99.35% of total MHD oil. Major components are carvacrol (67.85%), thymol (16.18%), and o-cymene (3.00%). Thirty-nine components were identified, representing 99.10% of total HD oil. Major components were carvacrol (69.78%), thymol (16.08%), and β-bisabolene (2.01%).