Objective To explore the effect of andrographolide on proliferation, migration, stem cell properties and epithelial-mesenchymal transition process of triple negative breast cancer cells and its mechanism through in vivo and in vitro experiments. Methods Sulforhodamine B method was used to detect the Cell viability. Migration, the proportions of CD447CD24-""* and the proliferation level of cancer stem cells were detected by wound healing assay, flow cytometry andmanmospheres assay, respectively.Western blot was used to detect the effects of andrographolide on the expression levels of YAP, ANKRD1, NESTIN, NANOG, E-cadherin, Vimentin, N-cadherin, Fibrone-Ctin YAP,ANKRD1, NESTIN, NANOG, E-cadherin, Vimentin, N-cadherin, Fibronectin and p-YAPin MDA-MB-231 and 4T1 cells. The effect of andrographolide on proliferation of breast cancer cells in vivo and the tumorigenicity of mice were examined through tumor transplantation experiment in mice. The expressions of YAP and ANKRD1 of tumor in mice was detected by immunohistochemistry. Results In vitro experiment results showed that cell viability of MDA-MB-231 and 4T1 cellstreated with andrographolide was decreased. in a dose-dependent manner. Compared with the control group, the healing rate of cells, the proportions of CD44+/ CD24-"'"" andthe volume and the number of stem cell microspheres in MDA-MB-231 and 4T1 cells were reduced (P < 0.05 ) .After andrographolide treatment, the expressions of YAP, ANKRD1, NESTIN, NANOG, Vimentin, N-cadherin and Fibronectin in MDA-MB-231 and 4T1 cells were down-regulated. Meanwhile, while the expression of E-cadherin andp-YAP were increased.In vivo experiment results showed that Compared with the control group, tumor volume and weight decreased and tumor inhibitory rate increased significantly after Andrographolide intervention (P < 0.01). And the expression of YAP andANKRDl of tumor in mice decreased. Conclusion Androgra pholide may play a role against triple-negative breast cancer by regulating the Hippo/YAP pathway [ABSTRACT FROM AUTHOR]