The aim of this study was to evaluate expression of COX-1 in renal cell carcinoma (RCC) and its prognosticvalue. mRNA of COX-1 was detected in 42 paired RCC and adjacent normal tissues with quantitative realtimepolymerase chain reaction (qRT-PCR). Expression of COX-1 was also evaluated in 196 RCC sections and91 adjacent normal tissues with immunohistochemistry. Statistical analysis was performed to assess COX-1expression in RCC and its prognostic significance. The results of qRT-PCR showed mRNA levels of COX-1 inRCC tissues to be significantly higher than that in adjacent normal tissues (p < 0.001). Immunohistochemicalassays also revealed COX-1 to be overexpressed in RCC tissues (p < 0.001). Statistical analysis demonstrated highexpression of COX-1 was correlated with tumour size (p = 0.002), pathological stage (p = 0.003), TNM stage (p= 0.003, 0.007, 0.027, respectively), and tumour recurrence (p < 0.001). Survival analysis indicated patients withhigh expression of COX-1 had shorter survival time (p < 0.001), and COX-1 was an independent predictor. Thisis the first study to reveal overexpression of COX-1 in RRC and point to use as a prognostic marker in affectedpatients.