Objective To explore the effects and mechanisms of bone marrow mesenchymal stem cell(BMMSC)-derived exosomes(BMMSC-Exo)on hypoxia/reoxygenation(H/R)-induced injury in rat cardiomyocyte cell line(H9c2).Methods BMMSC-Exosomes were isolated by ultracentrifugation.The cells were divided into three groups:control,H/R,and H/R+BMMSC-Exo(H/R+Exo).A hypoxia/reoxygenation(H/R)injury model was es-tablished by exposing cells to 12 hours of hypoxia followed by 6 hours of reoxygenation.Flow cytometry was used to detect cell apoptosis,DHE staining was used to assess cellular ROS levels,JC-1 immunofluorescence staining was used to evaluate mitochondrial membrane potential,and Western blot was used to detect mitochondrial autophagy-re-lated proteins.Results BMMSC-Exo treatment significantly alleviated oxidative stress,restored mitochondrial mem-brane potential,reduced mitochondrial autophagy levels,and effectively decreased cardiomyocyte apoptosis.Conclu-sions Bone marrow mesenchymal stem cell-derived exosomes alleviate H/R-induced cardiomyocyte injury.