Melissa officinalis is a medicinal plant belonging to the Lamiaceae family. The essential oil of this plant is used in many fields such as medicine, food, perfumery and cosmetics. Heavy metals have become one of the main abiotic stress agents for living organisms because of their increasing use in the developing fields of industry and agrotechnics and high bioaccumulation and toxicity. Although a lot of information is available concerning the effects of heavy metals on plant growth and physiology, much less is known regarding their effects on the production of secondary metabolites. Cadmium is one of the heavy metals, Because of its high mobility and low concentration, it easily enters the food chain from the soil. In this study, the effect of various concentrations of cadmium chloride (0.10, 20 and 40 mM) on the total phenolic content of two months old seedlings was investigated. In this study, the stems of lemon balm are in sterile conditions was propagation on the medium ½(MS) was used. After 60 days, seedlings were removed from solid MS medium, the roots were cutting and cultured in liquid medium of MS 1/2 with different concentrations of cadmium. The cultivation was carried out in erlen( 250 cc) and was kept in an incubator shaker device. After one week of growth of the stems in the medium, sampling was done for the experiment. The results show a positive and significant effect of cadmium chloride on total phenolic content. Only there was no significant difference in the concentration of 10 μM compared to the control, but at the concentration of 20 and then 40 μm, respectively, the highest phenolic content was produced(1/7 and 1/3 fold). In general, changes in heavy metals in metabolic activities of plants may appear to be effective.