Abstract: Objective :To establish a cell line with stable co-expression of HER2 and ER and to study its biological activity. Methods Recombinant eukaryotic expression vector plasmid pcDNA 3.1-HER2 was constructed. It was transfected into ER expressing MCF-7 cells with lipofectamine. The positive cell clones had been obtained after selected by G418. The MCF-7 cell transfected with HER2-cDNA was determined by RT-PCR, immunocytochemistry and Western blot. The activation of transfected MCF-7 cells was observed by MTT assay and cell invasion assay. Results : The strong expression of HER2 in transfected MCF-7 cells was confirmed at mRNA and protein levels. The capability of proliferation and invasion was obviously enhanced. Conclusion :The recombinant expression vector containing HER2 is successfully constructed. After introduction of the vector into MCF-7 cells, the MCF-7 cell line co-expressing HER2 and ER has also been obtained, which would be helpful for further study on HER2 gene.