The DNA repair gene Ku70 plays a key role in the DNA double-strand breaks (DSBs) repair system. Defects in DSBs repair capacity can lead to genomic instability. We hypothesized that the Ku70 A-31G polymorphism (rs132770) was associated with the risk of renal cell carcinoma (RCC). In a hospital-based case-control study of 620 RCC patients and 623 cancer-free controls frequency matched by age and sex, we genotyped the functional polymorphism Ku70 A-31G (rs132770). Thirty-eight normal renal tissue samples with different genotypes were tested to estimate the Ku70 mRNA expression by real-time quantitative reverse transcription. Compared with the GG genotype, the GA and GA/AA genotypes had a significantly decreased risk of RCC [adjusted odds ratio (OR) = 0.62, 95% confidence interval (CI) = 0.44-0.87 for GA, and OR = 0.62, 95% CI = 0.45-0.86 for GA/AA]. The in vivo experiments with normal renal tissues revealed that a statistically significantly higher Ku70 mRNA expression was identified in samples with GA/AA genotypes compared with those with GG genotypes (p = 0.001). These results suggested that the Ku70 A-31G polymorphism is involved in the etiology of RCC and, thus, may be a marker for genetic susceptibility to RCC in the Chinese populations.