There is a growing interest in metal oxide nanoparticles with unanticipated features that are different from traditional materials to fulfill the demands of these applications. Nickel oxide (NiO) nanoparticles were created by sol-gel and co-precipitation methods. In this study, nickel oxide nanoparticles (NiO NPs) were prepared by co-precipitation using NiCl₂ salt as a source of nickel nanoparticles and sodium hydroxide solution as a precipitating agent at room temperature and via sol-gel using citric acid (C₆H₈O₇.H₂O) and n-propanol (C₃H₇OH). The nickel hydroxide Ni(OH)₂ precipitate was obtained, then it was calcinated at 500°C to obtain the nickel oxide nanoparticles (NiO NPs). The structural, morphological, and spectral properties were confirmed and investigated by using   FE-SEM, TEM, and XRD, respectively. The antibacterial activity of the nickel oxide nanoparticles was investigated against several pathogenic bacteria, including E. coli and Staphylococcus aureus using the well diffusion method. The results showed good to excellent activity.