The study reports determination of appropriate-development stage, its effects on herbage yield and essential oil content compositions of summer savory (Satureja hortensis L). The essential oil of summer savory was isolated by steam distillation and analysed by GC-MS. The results indicated that the highest dry leaf yield, fresh and dry herbage yield were obtained at post and full blooming stage. However, the highest essential oil content of 2.6% was obtained at full blooming stage. Major essential oil components of summer savory were determined as thymol, gamma-terpinene, carvacrol and cymol in ratio of 47.9, 19.6, 14.7 and 9.7%, respectively. Thymol percentage increased at post harvest stage, in contrast to gamma-terpinene. The results suggest that to achieve maximum oil yield for profitable income harvest should be done at full blooming stage.