Thymus leucospermus Hartvig is a Greek endemic species of Section Teucrioides Jalas. The essential oils obtained from five populations growing wild in the National Park of Northern Pindhos (NW Greece) were studied. The oil content ranged between 1.1 and 2.0 mL per 100 g of dry plant weight. The oils were particularly rich in phenolic monoterpenes: they had a high thymol (64.7-92.0%) or carvacrol (93.4%) content, whereas in one of the oils considerable amount of both compounds was found (thymol 61.6% and carvacrol 26.4%). Our results show that T. leucospermus is a high-quality thyme species, with respect to both oil content and composition.