Abstract: The alleviating effects of iron (Fe) supplementation on zinc (Zn) toxicity were investigated in hydroponic Solanum nigrum seedlings. Hydroponic method was used to raise S. nigrum seedlings with three combined Zn and Fe concentrations - of 400 μmol·L^-1 Zn, 0 μmol·L^-1 Fe, 400 μmol·L^-1 Zn + 200 μmol·L^-1 Fe and standard 0.5 Hoagland nutrient solution as the control. The results showed that seedling height, root length and chlorophyll content reduced while H₂O₂ accumulation significantly increased in Zn-treated S. nigrum seedlings. Supplementation with Fe did not only improve Zn tolerance, but also increased gene expression and enzyme activities of SOD, CAT and APX in S. nigrum seedlings. RT-PCR results showed that supplementary Fe significantly increased FeSOD2 and CAT1 genes expressions. These results indicated that Zn toxicity-induced oxidation damage and growth inhibition were largely due to Zn-induced Fe deficiency in plants. Supplemental Fe in Zn-poisoned conditions improved FeSOD2 and CAT1 genes expressions. This enhanced antioxidant enzyme activity and reduced reactive oxygen species (ROS) level and oxidative damage of plants. The study provided the theoretical basis for further studies on molecular mechanisms of plant response to Zn toxicity and the practical applications for phytoremediation technology.