Abstract: Objective To examine the expression of MAGE-A4 (melanoma antigen-A4) mRNA in normal and breast cancer tissues and investigate the relationship between MAGE-A4 expression and the clinical and biological parameters and the effect of MAGE-A4 on the proliferation of breast cancer cells. Methods Expression of MAGE-A4 mRNA in 77 cases of normal breast tissues and breast cancer tissues were examined by RT-PCR. The relationship between MAGE-A4 expression and the clinical and biological parameters was analyzed by χ2 test. Colony formation assay was used to examine the effect of MAGE-A4 on the proliferation of breast cancer cells. Results There were no MAGE-A4 mRNA expressions in the 77 normal breast tissues. Thirty-three of 77 cases of breast cancer tissues expressed MAGE-A4 mRNA, with an expression rate of was 42.9%. There was no relationship between MAGE-A4 and tumor size, clinical stage, the type of pathology, histological stage, tumor embolus, ER/PR as well as HER-2 state (P>0.05). However, MAGE-A4 mRNA expression rate was higher in the breast cancer patients more than 60 years old than in the patients less than 60 years old (P<0.05)。MAGE-A4 mRNA was highly expressed in MDA-MB-436 cells, whereas there were no expressions of MAGE-A4 in MCF-7 and MDA-MB-231 cells at mRNA level. MAGE-A4 suppressed the colony formation in MCF-7 and MDA-MB-231 cells (P<0.05). Conclusion As a tumor specific antigen, MAGE-A4 was expressed in breast cancer tissues, but not in normal breast tissues. MAGE-A4 expression was correlated to patient's age. However, it was not correlated to other clinical and biological parameters. MAGE-A4 transfection into MCF-7 and MDA-MB-231 cells that did not express MAGE-A4 suppressed the colony formation of these cells.