Experiment was carried out at field of Medicinal Plant Research Center In Karaj city (Iran) in 2007. Four net N fertilizer levels were used including 0, 50, 100 and 150 kg/ha. The garden thymus aerial parts were harvested in full blooming time. In order to drying, the samples were placed at shade (room temperature). The aerial parts essential oil was extracted by hydro-distillation in Clevenger apparatus and analyzed by GC/MS. Results showed that nitrogen fertilizer had significant effect on essential oil of thymus vulgaris so that plants grown at 100 kg/ha nitrogen fertilizer had the highest essential oil (1.57% ). The N levels had significant effect on growth traits, essential oil and its composition. The maximum (15.3%) and minimum (2.5%) content of thymol were observed at 100 kg/ha and 0 kg/ha of N levels respectively. There was also positive correlation between N fertilizer and carvacrol content. The maximum (14.2%) and minimum (8.6%) contents of carvacrol were related to 100 kg/ha and 0 kg/ha of N levels respectively. The results showed that there were significant correlations between chemical character of soil and medicine ingredients material. There were positive correlation among essential oil percent and nitrogen, potassium and phosphorous elements.

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