Research on the qualitative and quantitative composition of essential oil was conducted in south-eastern Po-land. The aim of the study was to evaluate the chemical composition of essential oil from Satureja montana L. depending on the plant’s developmental stage. Seedlings of winter savory were planted in the field at a spac-ing of 30×30cm. The herb was collected on the following dates: June (vegetative stage of the plant), mid-Ju-ly (onset of flowering), mid-August (full flowering), and September (senescence). The highest essential oil content was found in plants at full flowering (1.88–2.20%) and at the beginning of flowering (1.63–2.20%). The oil from S. montana contained high levels of phenolic compounds, mainly carvacrol and thymol. The highest levels of carvacrol were found at the beginning of flowering (60.97–72.03%) and at full flowering (62.36–73.54%). The highest thymol content was found in 2018 – 19.47% – in the herb collected from plants that had finished flowering and 14.90% – in the herb from plants collected during the vegetative phase