Background: Platelet-rich plasma (PRP) helps promote wound healing, but it is unclear whether it stimulates breast cancer cell proliferation, which restricts its application in breast cancer patients. This article explored the effect of PRP on breast cancer cell proliferation through preclinical experiments. Method: We cultivated MDA-MB-231 breast cancer cells with PRP in vitro. Subsequently, we employed Cell Counting Kit-8 (CCK-8) assays to assess their proliferation ability, wound healing assays to evaluate their migration ability, and Transwell assays to detect their invasion ability. Mouse breast cancer 4T1 cells were subcutaneously inoculated into nude mice. After tumor formation, PRP was injected around each tumor. Tumor size was measured. After 15 days, the tumors were surgically removed. Immunohistochemistry was used to detect key proteins involved in proliferation and apoptosis. Results: PRP inhibited the proliferation, migration, and invasion of MDA-MB-231 in vitro. After PRP was injected around tumors in nude mice, tumor growth slowed, Ki67 and phospho-histone H3 (pHH3) expression decreased, and Caspase 3 and Poly (adenosine diphosphate-ribose) polymerase 1 (PARP1) expression increased. Conclusion: The PRP inhibits the proliferation of breast cancer MDA-MB-231 and 4T1 cells.