Iron is one of the effective constraint in plants that its role in enzyme activation has been identified. This investigation was done with basil (ocimum basilicum) in vegetative stage. Addition of iron to the soil of basil was carried out with 21 ppm during 6 days. The growth plant and the composition of its essential oil was subjected to study. Increasing iron supply resulted in decreased plant growth. The major compounds of essential oil of control plants were methyl chavicol, geraniol and nerol, respectively. However after treating with iron, the relative content of methyl chavicol was decreased, compared to the content of geraniol. The amount of caryophyllene oxide in treated plants was significantly higher than it in control plants. It can be concluded that excess iron supply reduced both growth of basil and the yield of its essential oil.