Objective:To integrate the two elements of selenium and magnesium into nanoparticles to prepare selenium-magnesium nanoparticles, and explore their antibacterial effect and antibacterial mechanism.Methods:The morphology and particle size distribution of selenium-magnesium nanoparticles were characterized by transmission electron microscopy and particle size analyzer. The antibacterial effect of selenium-magnesium nanoparticles was evaluated by plate counting method, disk diffusion method, and bacterial live/dead staining method. The content of reactive oxygen species in bacteria after exposure to nanoparticles was detected by DCFH-DA fluorescence probe to explore its potential antibacterial mechanism.Results:Selenium-magnesium nanoparticles are irregular spherical under transmission electron microscopy, and the particle size is mainly concentrated in the range of 50-70 nm. They exhibit excellent antibacterial properties, especially against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus. The potential antibacterial mechanism involves induction of reactive oxygen species production in bacteria.Conclusion:The prepared selenium-magnesium nanoparticles exhibit good antibacterial properties, it has been preliminarily demonstrated that bacterial killing is achieved by inducing the production of reactive oxygen species within bacterial.