Genetic diversity of common thyme (Thymus pulegioides L.) and wild thyme (Thymus serpyllum L.) by the RAPD method was evaluated. The investigated populations of both species significantly differed in respect of developmental traits as well the content and composition of essential oil. The content of essential oil in the herb Thymus pulegioides was higher. Phenolic substances (thymol and carvacrol) dominated in the essential oil of Thymus pulegioides, whereas terpens (β-myrcene, cineol, borneol and β-cariophyllene) in the essential oil of Thymus serpyllum.