Accumulating evidence suggests a pathogenic role of chronic hypoxia in various kidney diseases. Chronic hypoxia in the kidney was induced by unilateral renal artery stenosis, followed 7 days later by observation of tubulointerstitial injury. Proteomic analysis of the hypoxic kidney found various altered proteins. Increased proteins included lipocortin-5, calgizzarin, ezrin, and transferrin, while the decreased proteins were -2u globulin PGCL1, eukaryotic translation elongation factor 1-2, and Cu/Zn superoxide dismutase (SOD-1). Among these proteins, we focused on Cu/Zn-SOD, a crucial antioxidant. Western blot analysis and real-time quantitative PCR analysis confirmed the down-regulation of Cu/Zn-SOD in the chronic hypoxic kidney. Further, our laser capture microdissection system showed that the expression of Cu/Zn-SOD was predominant in the tubulointerstitium, and was decreased by chronic hypoxia. The tubulointerstitial injury estimated by histology and immunohistochemical markers was ameliorated by tempol, a SOD mimetic. This amelioration was associated with a decrease in levels of the oxidative stress markers, 4-hydroxyl-2-nonenal and nitrotyrosine. Our in vitro studies utilizing cultured tubular cells revealed a role of TNF- in down-regulation of Cu/Zn-SOD. As the administration of anti-TNF- antibody ameliorated Cu/Zn-SOD suppression, TNF- seems to be one of the suppressants of Cu/Zn-SOD. In conclusion, our proteomic analysis revealed a decrease in Cu/Zn-SOD, at least partly by TNF-, in the chronic hypoxic kidney. This study, for the first time, uncovered maladaptive suppression of Cu/Zn-SOD as a mediator of a vicious cycle of oxidative stress and subsequent renal injury induced by chronic hypoxia.