Essential oil and Menthol content were isolated from leaf samples of Mentha arvensis L. collected during March-November from the Medicinal Plants Farm Pakistan Forest Institute, Peshawar. Physico-chemical characteristics of the oil were also determined. October collection the oil were also determined. October collection gave high yield of oil (2.8%) and menthol content (68.0%) as compared to other periods of the year, next high yield of oil and Menthol content was observed in the month of August.