The waterdistilled essential oil from dried aerial parts of one of the Algerian thymes, Thymus fontanesii Boiss. & Reut. grown in Setif province, Algeria, was analyzed by GC/MS. Fifteen components were characterized representing 99.4% of the total components detected. The major components of the oil were thymol (67.8%), gamma-terpinene (15.9%) and p-cymene (13.0%).