Objective:To analyze the inhibiting mechanism of microRNA-199a/b-3p(miR-199)on cell proliferation of triple negative breast cancer(TNBC)cells.Methods:Expression of miR199 in BT549 and MDA-MB-231 cells transfected with miR-199a/b-3p was detected by qRT-PCR.The proliferation of BT549 and MDA-MB-231 cells transfected with miR-199 were analysed by MTT as-say.Cell cycle of TNBC cells transfected with miR-199 was detected by Flow Cytometry assay.Results:MiR-199a/b-3p could suppress the proliferation of BT549 and MDA-MB-231 cells.Comparing with normal control,the proliferation rate were up to(41.02±2.34)%and(28.42 ±6.70 )%,and the cell cycle were arrest at G 1 phase.Conclusion: MiR-199a/b-3p could suppress the proliferation of TNBC,and may be a promising anti-cancer drug for TNBC.