abstract the aerial parts of satureja sahandica bornm. were collected in three stages of plant growth (at the beginning of, full and end of flowering stage) from ghazvin province in the north of iran. the essential oils were isolated by hydrodistillation from the aerial parts of the plant material. the oils were analyzed by capillary gc and gc/ms. the highest oil yield was obtained at the beginning of flowering (3.30% w/w), then the oil content decreased to 2.28% at full flowering stage and more decreased (1.65%) at the end of flowering. twenty-three compounds were identified in the oil of s. sahandica at the beginning of flowering with -terpinene (42.3%), thymol (34.6%) and p-cymene (11.7%) as main components. twenty-three constituents were characterized in the oil of full flowering stage with p-cymene (30.2%), thymol (29.6%) and -terpinene (27.7%) as major components. twenty-seven compounds were identified in the oil at the end of flowering with p-cymene (58.1%), thymol (19.3%) and -terpinene (9.3%) as main components. the results showed, the percentage of p-cymene was increased in the oil of satureja sahendica with growth of the plant and during flowering period and the percentage of thymol and -terpinene have been reduced. so, harvesting of satureja sahendica can be commented at the beginning of flowering because of higher oil content and percentage of thymol.