Silicon (Si) is the second most abundant element in the soil, presents as silicic acid in soil solution. Although silicon has not been considered as an essential element for higher plants, it has been proved to be beneficial for the healthy growth and development of many plant species, particularly graminaceous plants. The beneficial effects of silicon are distinct in plants exposed to abiotic and biotic stresses. Heavy metals such as nickel and cadmium are entered to the soils as the results of human activities, causing great environmental problems. In fact heavy metals by accumulation in plants, not only causing damage to the plants, but also directly or indirectly enter to the the human and animal food chain and threaten their health. The main objective of the present study was to elucidate the beneficial effects of silicon on alleviation of oxidative damages caused by nickel and cadmium toxicity in two wheat cultivars (durum and back cross) in a hydroponic experiment. In this study, silicon was supplied as sodium silicate solution in two levels (0 and 1 Mm), Six concentration levels of nickel and cadmium (0, 2.5, 5, 10, 30 and 50 µM) and (0, 5, 10, 30, 50 and 100 µM) were supplied as NiCl 2 and CdCl 2 respectivily. After 60 days, the plants were harvested and the dry weight, concentrations of nickel, cadmium, silicon, iron and zinc in shoot and root, antioxidant enzyms activity (CAT and POX) and electrolyte leakage (EL) were determined. The results of this study indicated that regardless of cultivar, Si at 0, 2.5 and 5 µM of Ni treatments and at 0, 5 and 10 µM of Cd treatments increased shoot dry weight, and Si at 2.5 and 5 µM of Ni treatments and at 5 and 10 µM of Cd treatments increased root dry weight. Not regarding the cultivar, Si at 2.5 and 5 µM of Ni treatments and 5 and 10 µM of Cd treatments decreased shoot Cd and Ni concentrations. In durum cultivar, Si at 0 and 50 µM of Ni treatments and in back cross cultivar, at 0, 30 and 50 µM of Ni levels increased shoot iron concentration and Si at all Cd levels increased shoot iron concentration. In durum cultivar, Si at 0 and 2.5 µM of Ni and in back cross cultivar, in all Ni levels except for 10 µM level, increased shoot zinc concentration. Regardless of cultivar, Si at 0 and 5 µM of Cd treatments increased and in the other Cd levels decreased shoots zinc concentration. In durum cultivar, Si at all Ni levels except for 30 and 50 µM of Ni concentrations and in back cross, at 0, 2.5 and 5 µM of Ni levels increased catalase activity. While in durum cultivar, Si at all Ni levels except for 2.5 and 5 µM, increased peroxidase activity, in back cross cultivar , Si at all Ni treatment levels decreased peroxidase activity. In durum cultivar, Si at all Cd treatments except for 5 and 10 µM, and in back crosses cultivar at all Cd levels, increased catalase activity. Also in durum cultivar, Si at all Cd levels except for 100 µM and in back cross cultivar at 0 and 5 µM of Ni increased peroxidase activity. Regardless of cultivar, Si at 0, 2.5 and 5 µM of Ni treatments and 0, 5 and 10 µM of Cd concentrations decreased electrolyte leakage and in the other levels increased electrolyte leakage. According to the results, the effects of silicon on alleviation of heavy metal toxicity, depending on the type and concentrations of heavy metal and wheat cultivars were different. Key Words: Heavy metal pollution, Silicon, Nickel, Cadmium, Oxidative damage, Durum , Back cross , Wheat