In this research, Magnesium oxide nanoparticles (MgONPs) was prepared from MgCl2 solution using aqueous extract of M. oleifera bark as green agent. Preparation procedure involved mixing of MgCl2. 6H2O solution and the aqueous extract of M. oleifera bark, followed by drop wise addition of NaOH solution. The formation of MgO nanoparticles in this synthesis was confirmed using UV-Vis absorption. The spherical crystal structure of MgO nanoparticle confirmed XRD analysis. The average particle size of the synthesized MgO nanoparticles measured between 60-100 nm using SEM and TEM images and PSA results. MgONPs synthesized showed good antioxidant activity and antibacterial activity against S. aureus, E. faecalis, E. coli, and S. dysenteriae bacteria.