By investigating the effects of miR-379-5p on the proliferation, invasion and metastasis of mouse breast cancer 4T1 cells, we provide new therapeutic targets for clinical inhibition of breast cancer proliferation, invasion and metastasis. Methods After plasmid transfection, 4T1 cells were utilized to detect the expression of miR-379-5p using real-time fluorescence quantitative polymerase chain reaction (qRT-PCR); 5-ethynyl-2' doxyuridine (5-ethynyl-2'-deoxyuridine, EdU) cell proliferation assay and Transwell assay to detect changes in proliferation and invasion ability of 4T1 cells in each group; Migration ability of 4T1 cells after overexpression and knockdown of miR-379-5p was examined by scratch healing assay; BABL/c mice were used to establish the transplanted tumor model of breast cancer mice, and the tumor growth in vivo after miR-379-5p overexpression was observed.The transplanted tumor model of breast cancer was established in BABL/c mice, and the effects of overexpression of miR-379-5p on tumor growth and the number and size of lung metastases were observed . Results EdU results showed that knockdown of miR-379-5p enhanced the proliferation ability of cells compared with the control group, and miR-379-5p overexpression reduced the capacity of breast cancer cells to proliferate (p<0.05). Transwell and wound healing assays showed that knockdown of miR-379-5p enhanced the invasion and migration ability of breast cancer cells, and overexpression of miR-379-5p significantly inhibited the invasive and migratory ability of cells (p<0.01). In vivo tumorigenesis experiment of BABL/c mice showed that overexpression of miR-379-5p could significantly slow down the growth rate of tumor (p<0.05) and inhibit lung metastasis (p<0.01 ).In vivo experiments demonstrated that overexpression of miR-379-5p significantly slowed tumor growth (p<0.05). Conclusions miR-379-5p plays the role of tumor suppressor gene in breast cancer and inhibits the proliferation, invasion and migration of mouse breast cancer 4T1 cells.