To investigate the effect and mechanism of raddeanin A(RaA) in treating breast cancer.Methods:Breast cancer MDA-MB-231 cells were cultured in vitro and treated with RaA and RaA combined with n-acetylcysteine(NAC)，respectively.The changes of related proteins and signaling pathways were then examined.Results:Compared with the control group，RaA inhibited the proliferation，induced the apoptosis，promoted the mitochondrial membrane potential collapse，and elevated the reactive oxygen species(ROS) level of MDA-MB-231 cells(P<0.01).In addition，RaA increased the Bcl-2-assicated X protein(Bax)/B-cell lymphoma 2(Bcl-2) ratio(P<0.01)，up-regulated the protein levels of cytochrome C(Cyt-C)，cleaved CASP3(CCASP3)，and cancer suppressor gene 53(P53)(P<0.05，P<0.01)，and down-regulated the phosphorylation level of signal transducer and activator of transcription 3(STAT3)(P<0.05，P<0.01) in MDA-MB-231 cells.Compared with the RaA group，NAC combined with RaA lowered the ROS level，decreased the Bax/Bcl-2 ratio，down-regulated the protein levels of Cyt-C，CCASP3，and P53，and up-regulated the phosphorylation level of STAT3 in MDA-MB-231 cells(all P<0.01).Conclusion:RaA exerted the anti-breast cancer effect in vitro by activating the ROS/STAT3/P53 signaling pathway to induce mitochondrial apoptosis.