Objective:To determine the effect of rice bran extract (RBE) in combination with doxorubicin on 4T1 triple-negative breast cancer cells and NIH-3T3 cells. Methods:RBE was obtained by maceration with n-hexane. The phytochemical profile of RBE was observed using high-performance liquid chromatography. Cytotoxic effect of RBE was evaluated through MTT assay. In addition, flow cytometry was used for cell cycle and apoptosis analysis. Cellular senescence was observed using SA-β-Gal assay and intracellular reactive oxygen species (ROS) levels were evaluated using DCFDA staining. The pro-oxidant property of RBE was also evaluated through 1-chloro-2,4-dinitrobenzene spectrophotometry and molecular docking. Results:RBE was obtained with a yield of 18.42％ w/w and contained tocotrienols as the major compound. RBE exerted no cytotoxic effect on 4T1 and NIH-3T3 cells. However, RBE in combination with doxorubicin decreased 4T1 cell viability synergistically (combination index<0.9) and induced apoptosis and senescence on 4T1 cells. RBE significantly decreased senescence in doxorubicin-treated NIH-3T3 cells. Additionally, RBE did not increase ROS levels in doxorubicin-treated 4T1 cells. Meanwhile, the combination of RBE and doxorubicin reduced ROS levels in NIH-3T3 cells. RBE significantly reduced glutathione-S-transferase activity and alpha-tocotrienol interacted with glutathione-S-transferase in the glutathione binding site. Conclusions:Rice bran may be used as a co-chemotherapeutic agent to improve the therapeutic effectiveness of doxorubicin while protecting against the cellular senescence effects of doxorubicin on healthy cells.