Background: TGF-${eta}$-activated kinase-1 (TAK1) has been found to be over-expressed in a variety of solid malignancies and related to tumor growth. The aim of this study was to evaluate the expression level of TAK1 in clear cell renal cell carcinoma (ccRCC) and assess its value as a novel prognostic marker. Methods: TAK1 mRNA was assessed in 51 paired ccRCC tissues and adjacent normal tissues (ADTs) by real-time PCR. Tissue TAK1 protein was also assessed in 91 ADTs and 177 samples of ccRCC immunohistochemically for evaluation of relationships with clinical characteristics. Results: RT-PCR showed that TAK1 RNA level was significantly higher in ccRCC tissues than in the paired ADTs and immunohistochemistry confirmed higher expression of TAK1 protein in ccRCC samples compared with ADTs. TAK1 protein expression in 177 ccRCC samples was significantly correlated with T stage, N classification, metastasis, recurrence and Fuhrman grade, but not age and gender. Patients with low TAK1 levels had a better survival outcome. TAK1 expression and N stage were independent prognosis factors for the overall survival of ccRCC patients. Conclusions: Overexpression of TAK1 predicts a poor prognosis in patients with ccRCC, so that TAK1 may serve as a novel prognostic marker.