Objective: To investigate the relationship between estrogen receptor (ER) and epidermal growth factor receptor (EGFR), and its role and mechanism in tamoxifen (TAM) therapy resistance of breast cancer. Methods: Two types of cells namely the TAM therapy-sensitive (TAM-S) and -resistant (TAM-R) human breast cancer MCF-7 cells were used. In these two types of cells, immunoprecipitation (IP) was performed to detect the connection between ERα and EGFR, and the connection of c-Src to the two former receptors, and the phosphorylation level of c-Src was also determined by Western blot analysis. After treatment with c-Src inhibitor PP2, the connection between ERα and EGFR was examined again by IP method. Results: ERα and EGFR linked in a complex form in both types of cells, but the linkage level in TAM-R cells was significantly higher than that in TAM-S cells (P<0.05). c-Src linked in a complex form to either ERα or EGFR in both types of cells, and the phosphorylation level of c-Src in TAM-R cells was significantly higher than that in TAM-S cells (P<0.05). After the c-Src activity was inhibited by PP2, linkage level between ERα or EGFR was decreased in both types of cells, while the decreasing degree in TAM-R cells was significantly greater than that in TAM-S cells (P<0.05). Conclusion: There is a connection between ERα and EGFR, which may play an important role in TAM therapy resistance of breast cancer, and c-Src activation (phosphorylation) may be the crucial mechanism for their linkage.