Objective：To investigate the clinical value of PAX5 promoter methylation as a biomarker of prostate cancer. Methods：The expression of PAX5 mRNA in prostate cell lines（RWPE-1，LNCaP，PC-3，and DU145）was detected by real time RT-PCR. Methylation-specific PCR（MSP）was used to analyze the methylation status of four prostate cells Real-time RT-PCR was used to detect the expression of PAX5 mRNA in tumor cells. Real-time MSP was used to detect the expression of PAX5 gene in 64 cases of prostate cancer，22 cases of benign prostatic hyperplasia and 47 healthy controls. The methylation level of PAX5 gene promoter in the serum of patients with prostate cancer was analyzed by ROC curve. The methylation level of PAX5 gene promoter in the serum of patients with prostate cancer was analyzed statistically. Results：Real-time RT-PCR showed that PAX5 mRNA was down-regulated in three prostate cancer cells compared with normal prostate epithelial cell RWPE-1；PAX5 gene promoter was detected in LNCaP，PC-3 and DU145 prostate cancer cells. Methylation of PAX5 gene promoter in normal prostate epithelial cell RWPE-1；the expression of PAX5 gene mRNA was restored by demethylation drug；Real-time MSP result showed that the methylation level of serum PAX5 gene promoter of prostate cancer patient was significantly higher than that of benign prostatic hyperplasia patients and healthy subjects. The methylation rate of PAX5 gene promoter was correlated with Gleason score and TNM staging；ROC results showed that the diagnostic value of PAX5 gene was superior to that of PSA. Conclusion：The methylation status of PAX5 gene in prostate cancer cells is the main reason for the down-regulation of PAX5 gene expression. Methylation of PAX5 promoter is a potential marker for prognosis of prostate cancer.