Objective: To investigate c-Src expression in breast cancer resistant to tamoxifen (TAM) therapy and its significance. Methods: The expression and phosphorylation level of c-Src in TAM-resistant and sensitive human breast cancer MCF-7 cells were detected by Western blot analysis. The apoptosis in these two cell lines was detected by enzyme-linked immunosorbent assay (ELISA) and acridine orange/ethidium bromide (AO/EB) double fluorescent staining after treatment with c-Src inhibitor PP2. Results: Compared with TAM-sensitive MCF-7 cells, the levels of c-Src expression and phosphorylation in TAM-resistant MCF-7 cells were significantly increased. After exposure to PP2, the enrichment factor and cell apoptotic rate in TAM-resistant MCF-7 cells were significantly higher than those in TAM-sensitive MCF-7 cells (both P<0.05). Conclusion: There is a higher c-Src expression and activity in human breast cancer MCF-7 cell lines resistant to TAM therapy, which may probably be associated with the mechanism of endocrinotherapy resistance of breast cancer.