In order to evaluate the effect of phenological stage on quantitative and qualitative variations in the content and composition of Thymus daenensis Celak essential oil, plant material has been collected from nature in Malayer city at four growth stages (vegetative stage, budding stage, flowering stage and seed bearing stage). Essential oil was extracted from air dried plants by hydrodistillation method for 3 hours. Analysis of the essential oil was carried out by GC and GC-MS. Results indicated that the maximum essential oil yield (3.4 %) was obtained in flowering stage. The major components of essential oil in all growth stages were thymol, α-terpinene, p-cymene, methyl carvacrol and α-Thujene. The higher percentage of thymol (73.8 %) was obtained in flowering stage, α-terpinene (9.59 %) in vegetative stage, p-cymene (9.0 %) and Methyl carvacrol (4.9 %) in seed bearing stage and α-thujene (1.42 %) in budding stage.
