Abstract: The research is aimed to investigate the effect of genistein (GEN) on the apoptosis in lipopolysaccharide (LPS)-activated RAW264.7 cells and explore the pharmacological mechanism of GEN anti-atherosclerosis (AS). RAW264.7 cells were activated by LPS, the level of TNF-α and IL-6 mRNA were detected by qRT-PCR, the expression of COX-2 and iNOS were detected by Western blot. RAW264.7 cells were pretreated with GEN for 2 h, and then incubated with LPS for 24 h. After that, CCK8 kit was used for the cell viability, Annexin V-FITC/PI kit for the apoptosis of cell. qRT-PCR was used to detect the level of CHOP, caspase-3 and miR-21. Western blot was used to detect the expression of CHOP and caspase-3. Results showed that LPS (1 000 ng·mL^-1) increased the expression of TNF-α, IL-6, COX-2 and iNOS in RAW264.7 cells compared with that in control group. GEN inhibited the cell activity and the level of miR-21, promoted the expression of CHOP and caspase-3 in LPS-activated RAW264.7 cells in a dose-dependent manner. miR-21 up inhibited the expression of CHOP and caspase-3 in LPS-activated RAW264.7 cells and this process was reversed by GEN treatment. miR-21 down promoted the expression of CHOP and caspase-3, which were further enhanced by GEN. These results indicate that GEN promotes the apoptosis of RAW264.7 cells activated by LPS through down regulating miR-21 and activating endoplasmic reticulum (ER) stress pathway.