Objective To investigate the effect of over-expression of monocarboxylate transporter (MCT) on biological behavior of breast cancer MDA-MB-231 cells. Methods Breast cancer MDA-MB-231 cells were transfected with eukaryotic expression plasmid pcDNA3.1/MCT (experiment group) and blank plasmid pcDNA3.1 (negative control group), and cells without treatment were served as blank control group. The transfection efficacy of MCT gene was detected by Real-Time PCR and immunofluorescence method. The effect of MCT gene transfection on proliferation of cells was determined by MTS method, and the morphological changes of cells were examined by acridine orange fluorescent staining. The effect of over-expression of MCT on apoptosis, necrosis and cycle of cells was determined by flow cytometry. The effect of MCT gene transfection on invasion and metastasis of cells was examined by Transwell test. Results The expression of MCT gene and protein in experiment group was significantly higher than that in negative control group and blank control group (P<0.01). The over-expression of MCT gene inhibited the proliferation of cells, enhanced the apoptosis and necrosis of cells, decreased cells in G2 cycle and increased cells in S cycle, and inhibited the invasion and metastasis of cells (P<0.01 or P<0.05). Conclusion The over-expression of MCT gene may promote the apoptosis and necrosis of breast cancer MDA-MB-231 cells, regulate cell cycle, and inhibit the proliferation,  invasion and metastasis of cells.