Tumor necrosis factor-alpha (TNF-alpha) has been found to be centrally involved in the development of ischemia-reperfusion injury (IRI)-induced inflammation and apoptosis. Knockdown of TNF-alpha gene using small interfering RNA (siRNA) may protect renal IRI. Renal IRI was induced in mice by clamping the left renal pedicle for 25 or 35 min. TNF-alpha siRNA was administered intravenously to silence the expression of TNF-alpha. The therapeutic effects of siRNA were evaluated in terms of renal function, histological examination, and overall survival following lethal IRI. A single systemic injection of TNF-alpha siRNA resulted in significant knockdown of TNF-alpha expression in ischemia-reperfusion injured kidney. In comparison with control mice, levels of BUN and serum creatinine were significantly reduced in mice treated with siRNA. Pathological examination demonstrated that tissue damage caused by IRI was markedly reduced as a result of TNF-alpha siRNA treatment. Furthermore, survival experiments showed that nearly 90% of control mice died from lethal IRI, whereas more than 50% of siRNApretreated mice survived until the end of the eight-day observation period. We have demonstrated for the first time that silencing TNF-alpha by specific siRNA can significantly reduce renal IRI and protect mice against lethal kidney ischemia, highlighting the potential for siRNA-based clinical therapy.