Thymus eigii is a perennial shrub from Lamiaceae family and it is found as wild in Adana and Hatay provinces, Turkey. The potential use of Thymus spp. in the prevention of viral diseases is making its demand rise. In this study, T. eigii plants were collected at various growth stages (pre-flowering, mid-flowering, and full-flowering) from Adana, Turkey in order to determine the most suitable harvest time for the highest amount of essential oil and yield. Full-flowering resulted in the highest plant height (36.11 cm), plant diameter (57.30 cm), fresh herb yield (251.31 g plant-1), fresh flower yield (158.24 g plant-1), dry herb yield (84.73 g plant-1), and dry flowers yield (53.63 g plant-1), whereas the highest fresh leaves yield (38.97 g plant-1) and dry leaves yield (16.72 g plant-1) were found at mid-flowering. While the highest flower essential oil rate (4.75 ml 100 g-1) was obtained at mid-flowering, the highest leaves essential oil rate (2.77 ml 100 g-1) was found at pre-flowering. The major compounds were carvacrol (70.87-77.98%), p-Cymene (3.39-7.46%), β-Caryophyllene (3.90-5.17%), γ-Terpinene (0.58-5.15%), and isoborneol (0.30-3.58%). As a result, the most suitable harvest time was determined as pre-flowering in terms of dry leaf yield and full-flowering in terms of flowers essential oil yield.