Medicinal plants are considered as valuable Iranian genetic resources. Among these plants, the medicinal herb, Trachyspermum ammi , belongs to Apiaceae family, and is an annual plant and one of the oldest medicinal plants cultivated in different parts of the country. Fruit contains 2 to 9 percent of essential oil, in which 40 to 60 percent of the essential oil is thymol, and the rest is consisted of gametripenene, pecymon, and carvacrol. Stimulation of plants using magnetic fields is considered as a method to increase the quantity and quality of the product. For this reason, replacing fertilizers and chemical supplements with physical treatments reduces the amount of pesticides in vegetable raw materials and increases the health of food and the environment. The purpose of this study was to evaluate the effect of magnetic water and nitrogen fertilizer on functional traits and essential oil content of this plant in a factorial experiment based on a complete block desian with three replications based on irrigation with magnetic water, nitrogen fertilizer treatment, and their combinations. The experiment was carried out during the years 94-96 in a pot expriment in Chah-e-Anari Farm, Isfahan University of Technology. The genetic material included 23 accessions of the germplasm from the Institute for Research of Forests and Rangelands of Iran, which were collected in different parts of Iran and were previously caltivated at Isfahan University of Technology. The results obtained from the analysis of variance of morphological traits showed that there was a significant variation among the genotypes in relation to the all traits. The results of variance analysis of morphological traits revealed that there was a significant variation among the populations in terms of the type of treatment for the total traits. In the tested plants, grain yield and essential oil content were the most important traits for economic purposes. In the present study, the khorsar population under the treatment of magnetic water had the highest grain yield and thousand grain weight, and the Rafsanj population had the highest amount of essential oil. Analysis showed that the highest positive correlation was observed between days to 50% flowering and day to 100% flowering (0.97), seed yield per plant and seed number in umbel (0.91(, Days to 50% flowering and day to 100% flowering had a negative correlation with height (-0.61) and (-0.54) respectively. Thousand grain weight and days to 50% and day to 100% flowering showed negative correlation of (-0.51) and (-0.55), respectively. The percentage of essential oil had a negative correlation with day to 50% flowering (-0.61), and day to 100% flowering (-0.56). In general, in all conditions, based on cluster analysis, ecotypes were Key words: Ajowan, Magnetic water, Nitrogen fertilizer, Essential oil content