Objective:To analyze the expression and role of activated transcription factor 3 (ATF3) in breast cancer.Methods:The Cancer Genome Atlas\Gene Expression Omnibus (TCGA\GEO) database information was queried, the expression level of ATF3 in breast cancer was analyzed by bioinformatics method and the survival curve was drawn. the parallel function and pathway enrichment analysis of ATF3 gene interaction network were constructed.Results:The level of ATF3 mRNA in breast cancer was significantly lower than that in normal breast tissue, but the expression level of ATF3 was significantly increased after chemotherapy. Survival analysis found that after systematic treatment, the survival period of breast cancer patients in the ATF3 high expression group was significantly prolonged, and the difference was statistically significant ( P<0.05). Enrichment analysis revealed that breast cancer-related pathways concentrate in Estrogens signaling pathway, mitogen-activated protein kinase kinases (MAPK) signaling pathway, phosphatidylinositol 3-kinase-protein kinase B (PI3K-Akt) signaling pathway, Wnt signaling pathway, Breast cancer signaling pathway, and Cell cycle signaling pathway. Conclusions:ATF3 is involved in regulating the proliferation of breast cancer cells. After systematic treatment, the high expression of ATF3 indicates a better outcome.