AIM: To investigate the effect of 3-bromopyruvate cholesterol ester (3-BP-Cl) on the sensitivity of breast cancer to tamoxifen (TAM). METHODS: MTT assay and Calcein AM/PI staining were used to detect the effect of drugs on the viability of breast cancer cells. Kim's formula was used to detect synergistic anti-breast cancer effect of cholesterol 3-bromopyruvate and tamoxifen. The inhibitory effect of drugs on proliferation of breast cancer cells was detected by colony-forming assay. Flow cytometry was used to detect the apoptosis of breast cancer cells. Western blot assay was used to detect the expression of hexokinase 2, Bcl-2 and Bax proteins. RESULTS: MTT results showed that combination 3-BP-Cl and TAM could significantly inhibit the activity of MCF-7 cells (P<0.05). The results of King's formula showed that 3-BP-Cl and TAM had synergistic inhibitory effect on the proliferation of MCF-7 cells (q>1.15). Calcein AM/PI staining showed that the number of dead cells was the highest in the combination group. Colony-forming assay showed that the combination group had stronger inhibitory effect on the proliferation of MCF-7 cells than that of single drug groups. AnnexinV flow cytometry results showed that, the cell apoptosis in the combination group was significantly increased (P<0.01). Western blot results showed that 3-BP-Cl inhibited the expressions of hexoktokinase 2 and Bcl-2, and enhanced the expression of Bax in MCF-7 cells. CONCLUSION: 3-BP-Cl could increase the sensitivity of breast cancer cells to tamoxifen, and synergically inhibit the proliferation of breast cancer cells. The mechanism is possibly related to its effects of inhibiting the expression of HK2/Bcl-2, and enhancing the expression of Bax.