Abstract: We investigated the ability of 3-bromopyruvic acid to increase the sensitivity of tamoxifen-resistant MCF-7/TR cells to tamoxifen and to explore the underlying mechanism. 4-Hydroxy tamoxifen (4-OHT) is the active form of tamoxifen in vivo and was used in this study. The effect of 3-bromopyruvic acid on the viability of MCF-7/TR cells was measured by MTT assay and the morphology of MCF-7/TR cells was observed with an inverted microscope. The results show that 3-bromopyruvic acid at 40 μmol·L^-1 has no significant effect on the viability of MCF-7/TR cells, and this concentration was used in the subsequent experiments:3-bromopyruvic acid significantly increased the inhibitory effect of 4-OHT on the viability of MCF-7/TR cells, with a reversal-fold of 1.91, as determined by MTT assay; the lactate level, determined with a lactate detection kit, and the expression levels of GLUT1, HK2, and LDHA in MCF-7/TR cells as measured by immunoblotting were significantly higher than in MCF-7 cells; and compared with 4-OHT treatment alone, the combination treatment of 3-bromopyruvic acid and 4-OHT significantly reduced the lactate level and the expression of GLUT1, HK2, LDHA in MCF-7/TR cells. The above results show that 3-bromopyruvic acid increases the sensitivity of MCF-7/TR cells to tamoxifen, and the mechanism is related to the inhibition of aerobic glycolysis.