Abstract: Objective:To investigate the expression level and significance of miR-4804-3p in breast cancer tissues, observe its effect on the proliferation and migration of breast cancer cells, and preliminarily explore its mechanism.Methods:The expression level of miR-4804-3p in 40 breast cancer tissues and different breast cancer cell lines was analyzed by real-time fluorescence quantitative PCR (RT-qPCR), and the relationship between miR-4804-3p level and clinicopathological indexes was analyzed.The effect of miR-4804-3p on proliferation and migration of breast cancer cells was observed by cell counting kit-8(CCK-8)and scratch healing assay.Results:The expression level of miR-4804-3p in breast cancer tissues was significantly lower than that in adjacent tissues(P< 0.01), and its level was associated with TNM stage, lymph node metastasis, and complement C3 level(P < 0.05), negatively correlated with heat shock protein 90α and suppressor T lymphocyte levels(P< 0.05), and positively correlated with the number of B lymphocytes (P< 0.05).The expression level of miR-4804-3p in breast cancer cell lines was significantly lower than that in normal breast cells (P< 0.05).Overexpression of miR-4804-3p could inhibit the proliferation and migration of MDA-MB-231 triple-negative human breast cancer cells.Conclusion:The expression level of miR-4804-3p in breast cancer tissues and cells is significantly down-regulated and miR-4804-3p can inhibit the proliferation and migration of MDA-MB-231 cells.