The genus Achillea L. (Asteraceae) is widely distributed in Turkey and used as folk remedies for their several biological effects. In this study hydro distilled essential oils of Achillea biebersteinii and Achillea teretifolia were analysed by gas chromatography and gas chromatography-mass spectrometry (GC-MS) techniques, simultaneously. Piperitone (44.7%), 1,8-cineole (15.9%) and camphor (4.9%) were the main constituents of A. bibersteinii oil, while 1,8-cineole (18.8%), camphor (17.6%), p-cymene (13.7%) and chrysanthenone (10.2%) were the main constituents of A. teretifolia essential oil. The oils of A. biebersteinii and A. teretifolia were subjected to a screening for their antimicrobial activities by using broth microdilution technique. A. bibersteinii volatile oil showed an inhibitory effect at the concentrations ranging from 31.25 to >2000 1.mu g/mL while A. teretifolia oil was effective at 250 to >2000 mu g/mL. A. bibersteinii volatile oil remarkably inhibited the growing of Candida utilis and C. krusei pathogenic yeast at the doses of 31.25 and 125 mu g/mL respectively.