〔Abstract〕 Objective To investigate the effects and mechanisms of Astragalus Polysacharin (APS) on the proliferation and metastasis of breast cancer cells by regulating miR-107 and miR-346-mediated macrophage polarization in breast cancer-derived exosomes. Methods Forty 8-week-old female BALB/c mice were selected and breast cancer xenograft models and 4T1 transplanted tumor models were established. The mice were divided into the control group and the APS group. The APS group mice received daily intragastric administration of APS for 25 days, while the control group mice were given the same amount of normal saline. After all treatments were completed, the mice were euthanized, and tumor tissues were isolated. Western blot and flow cytometry were used to detect the expressions of proliferating cell nuclear antigen (PCNA), Ki-67, CD206, CD163, inducible nitric-oxide synthase (iNOS), and CD86. The apoptosis of single-cell suspensions in tumor tissues was analyzed. Human breast cancer cell line MDA-MB-231 was cultured and stimulated with APS, and exosomes from the cell culture medium were collected. The proliferation, migration, and invasion of cells were detected by CCK-8 assay, scratch assay, permeability chamber cell invasion assay, and qRT-PCR. Differentially expressed genes were screened by bioinformatics. ResultsBy measuring the expressions of molecules related to breast cancer cell proliferation and metastasis, it was shown that APS treatment reduced the expressions of proliferation-related proteins (PCNA and Ki-67) and metastasis-related proteins (Vimentin) in MDA-MB-231 xenograft tumor tissues; and the polarization of tumor-associated macrophages was observed. APS treatment of 4T1 transplanted tumor tissues could reduce the number of M2 macrophages and increase the number of M1 macrophages, resulting in an increase in the ratio of M1/M2 macrophages and an increase in cell apoptosis in 4T1 transplanted tumor tissues. The expressions of related proteins iNOS and CD86 increased, and CD206 and CD163 decreased. After APS treatment, the exosomes produced by MDA-MB-231 reduced the polarization of M2 macrophages and affected the expressions of miR-107 and miR-346. Conclusion APS inhibits the polarization of M2 macrophages by regulating the expression of miR-107 or miR-346 in breast cancer cell-derived exosomes, ultimately inhibiting the proliferation and metastasis of breast cancer cells.