The aim of this study was to determine the therapeutic potential of borax against copper in the kidney tissue of the rainbow trout fed with added borax (BX) (1.25, 2.5, and 5 mg/kg) and/or copper (Cu) (500,1000 mg/kg) contents. For this purpose, two treatment groups had designed, and glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) enzyme activities were determined. Besides, oxidative DNA damage (8-hydroxy-2 '-deoxyguanosine, 8-OHdG), caspase-3, and malondialdehyde (MDA) levels were assessed in kidneys of all treatment groups. In molecular pathway, hsp70, CYP1A, and antioxidant gene expression levels were determined. In the results of the analysis, antioxidant enzyme activity and gene expression were increased; 8-OHdG, caspase-3, and MDA levels were decreased in groups fed with borax supplemented feeds compared to the copper-treated group. The alterations among the groups were found as significant (p < 0.05). CYP1A and hsp70 gene expressions were upregulated in copper and copper combined groups (p < 0.05). The findings of present research showed that borax had alleviative effect on copper-induced toxicity and could be used as an antidote in fish nutrition.