A new mixed matrix Polyethersulfone (PES)-co-Magnesium oxide nanoparticles (MGO) nanocomposite nanofiltration membrane was prepared through phase inversion method by using polyvinylpyrrolidone (PVP) as pore former and N, N dimethylacetamide (DMAc) as solvent. The influence of MGO nanoparticles concentration in the membrane matrix on the separation performance and physico-chemical characteristics of prepared membrane was studied by scanning electron microscopy, surface analysis, porosity measurement, water contact angle, permeability flux, salt rejection, antifouling property, and tensile strength. SEM images exhibited situating of MGO nanoparticles on the top surface of mixed matrix prepared membranes. SEM analysis also showed formation of a dense nanoparticle layer on the surface of prepared membrane at high additive concentration. Surface analysis results that revealed membrane surface roughness was increased initially by addition of MGO and then was decreased. Measured porosity showed reduction behavior for all prepared membranes filled with MGO nanoparticles. The membrane surface hydrophilicity was enhanced 35% by incorporating MGO nanoparticles into the membrane matrix. Results showed that membrane permeation flux was improved 32% by utilizing of MgO nanoparticles into the membrane matrix. Salt rejection was also improved 49% by using MGO nanoparticles in the membrane matrix relatively. The modified membranes filled with different concentrations of MGO nanoparticles showed higher antifouling properties and tensile strength compared to the neat PES membrane.