Abstract: Objective: To investigate the effects and mechanisms of 2-dodecyl-6-methoxocyclohexa-2,5-dien-1,4- dione (DMDD) on apoptosis and autophagy in triple-negative breast cancer (TNBC) MDA-MB231 cells. Methods: MDA-MB-231 cells were divided into a control group and low-, medium-, and high-dose DMDD groups (7.5 μmol/L, 15 μmol/L, and 30 μmol/L). Cell proliferation was assessed using the cell counting kit-8 (CCK-8) assay and colony formation assay. Apoptosis was evaluated by flow cytometry, while autophagy was detected using an autophagic vesicle detection kit. Furthermore, the protein expression levels of PI3K, Akt, mTOR, LC-3-Ⅱ/LC-3-Ⅰ, p62, PD-1, and PD-L1 were determined by western blotting. Results: The CCK-8 assay results demonstrated that DMDD inhibited the proliferation of MDA-MB231 cells and a reduction in breast cancer cell colony formation was also observed (both P＜0.05). After DMDD treatment, the apoptosis and autophagy levels of breast cancer cells were significantly increased (both P＜0.05). Results from apoptosis and autophagy assays indicated increased levels of apoptosis and autophagy in breast cancer cells after DMDD treatment (both P＜0.05). Additionally, western blotting analysis revealed that DMDD decreased the protein expression levels of PI3K, Akt, mTOR, PD-1, and PD-L1, while increasing the expression levels of the LC-3-Ⅱ/LC-3-Ⅰ ratio and p62 protein (all P＜0.05). Conclusion: After DMDD treatment, the levels of apoptosis and autophagy are elevated in MDAMB231 cells, and this mechanism may be associated with the inhibition of the PI3K/Akt/mTOR signaling pathway and the downregulation of PD-1/PD-L1 expression.