Objective To investigate the effect of Yanghe decoction serum on the proliferation of breast cancer stem cells HMLER90hi and its mechanism. Methods Twenty female Sprague-Dawley rats were randomly divided into low,medium and high dose groups containing drug serum and control group, in order to prepare the Yanghe decoction serum and blank serum. After 24 hours of drug intervention,the effects of each group on the proliferation of HMLER90hi cells at 24 h,48 h,and 72 h were detected by MTT assay. The expression of EphA4 and p50 mRNA in each group were detected by real-time fluorescence quantitative PCR. Results Compared with the blank control group,the cell proliferation activity of each dose group of Yanghe decoction significantly decreased at 24 h (0.818 ± 0.061, 0.706 ± 0.073, 0.587 ± 0.052 vs. 0.928 ± 0.075), 48h (0.760 ± 0.047, 0.638 ± 0.056, 0.510 ± 0.059 vs. 0.973 ± 0.095), and 72 h (0.672 ± 0.102, 0.508 ± 0.092, 0.448 ± 0.048vs.1.023 ± 0.099) (P<0.05 orP<0.01), respectively. After 24 h of drug intervention, compared with the control group, the expression of EphA4 mRNA (0.54 ± 0.07, 0.54 ± 0.07, 0.33 ± 0.04 vs.0.68 ± 0.09) significantly decreased, and p50 mRNA (0.69 ± 0.10, 0.54 ± 0.08, 0.41 ± 0.06vs. 0.85 ± 0.13) significantly decreased in each dose group of Yanghe decoction (P<0.05 orP<0.01).ConclusionsTheYanghe decoction can inhibit the proliferation of breast cancer stem cell HMLER90hi,and its mechanism may be related to its inhibition of the conduction of the juxtacrine pathway of monocyte macrophage.