Abstract: Objective: To investigate the anti-tumor effects of a recombinant EGFR antisense adenovirus,AdE5,for breast cancer cells. Methods: Human breast cancer MDA-MB-231 cells were injected s.c.into right flanks nude mice.Two intra-tumoral injections of 100μl PBS buffer containing 10⁹ pfu of AdE5 or AdCO1 or PBS alone were practised.The growing tumors were measured,and relative gowth index were caculated.HE coloration was performed for histological study,and Ki-67 expression was determined by immunohistochemical staining. Results: The tumor growth was inhibited by AdE5 treatment（relative gowth index ＜ 1）.Histological analyses revealed that AdE5 caused an increase of central necrosis in tumor tissues.Immunohistochemical study showed that Ki-67 expression was significantly inhibited by AdE5 compared with AdCO1 or PBS. Conclusion: The transduction of EGFR antisense RNA by adenoviral vector is effective for inhibition of in vivo growth of breast cancer cells.