Pb poses a major threat to plant growth and silicon can reduce its toxicity. This work was conducted hydroponically as a completely randomized factorial design to study the effect of Si (70 and 140 ppm) on Triticum aestivum cultivars Chamran and Shiroudi under Pb stress (150 ppm). Pb caused significant increases in the H2O2, free amino acids and proline contents of wheat cultivars and MDA content of cv. Chamran. Furthermore, Pb stimulated the activities of SOD and APX in cv.