Abstract: Objective: To investigate methylation of the RIZ1 promoter in human breast cancer tissue and its significance in related clinical and pathological data, and to explore its relationship to RIZ1 mRNA expression. Methods: Methylation-specific PCR(MSP) was performed to detect the methylation status of the RIZ1 promoter in human breast paraneoplastic tissue specimens and in benign breast tumor tissue specimens. The results were analyzed in combination with the clinical and pathological data of the patients and the RT-PCR results. Results: Among the 34 breast cancer specimens,RIZ1 promoter methylation was detected in 15 cases (44.1%). No relationship has been found between RIZ1 promoter methylation and clinical parameters including age, TNM stages, lymph node metastasis or ER status (P>0.05 for each parameter). The expression of RIZ1 mRNA was found to be lower in the specimens with RIZ1 promoter methylation than in those specimens with promoters that were unmethylated (P<0.05). Downregulated RIZ1 expression had a correlation with hypermethylation of the promoter (P<0.05). Conclusion: Hypermethylation of the RIZ1 promoter is a frequent molecular pathological event in breast cancer. RIZ1 mRNA expression is downregulated when the promoter is hypermethylated.