Zinc (Zn
2+
) is one of the essential micronutrient elements for plant growth. In the present study, effect of different concentrations of zinc on some physiological and biochemical properties of basil (Ocimum basilicum) was investigated. Basil seedlings were exposed to six zinc (ZnSO
4
) levels (0, 50, 100, 200, 400, and 800 mg/L) in 3 days’ intervals for a period of 30 days. The root and shoot growth, leaf number and area, photosynthetic pigments content, total soluble sugars and proteins, phenolic compounds, antioxidant power and mineral elements contents including zinc and potassium were significantly increased in effect of zinc levels up to 200 mg/L. Inversely, ferrous and calcium contents was drastically decreased concomitant with increasing zinc concentration but magnesium content remained unchanged. Our results indicated a dual role of zinc with optimum concentration of 200 mg/L, and a decrease in the root and shoot growth, pigment and phenolic contents under and over optimum concentration, whereas sugars and protein accumulation were occurred concomitantly with increasing zinc in the medium. However, the decrease of these parameters at the highest zinc concentration did not reach the level of control plants, which means that this species has a high resistance against zinc metal stress and because of the relative accumulation of zinc in polluted areas may has an important role for human nutrition. In general, the results point to important role of zinc in maintaining and protecting of basil seedlings against radical oxygen species
