Introduction and Aim: Nanomaterials are tiny particles varying in size from 1-100 nanometers with wide implications in the fields of medicine, biology, and pharmaceutical sciences. In this study, we aimed to extract Nickel oxide nanoparticles (NiO-NP) from the tropical hibiscus plant, and evaluate these nanoparticles for their structural features as well as study the antimicrobial activity of NiO-NPs against Gram-positive and Gram-negative bacteria.   Materials and Methods: NiO nanoparticles were synthesized by green nanotechnology using hibiscus extract and nickel nitrate as precursors. The NiO nanoparticles obtained were investigated for its surface properties using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and UV-Vis analysis. Transmission Electron Microscopy (TEM) was used in calculating the size of NiO nanoparticles. The antimicrobial activity of the NiO particles was tested against E. coli and S. aureus test strains.   Results:  X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy studies confirmed the formation of pure and well- crystallized NiO nanoparticles. The TEM analysis displayed that the size of nanoparticles to be within the limits of 71. The NiO-NP particles displayed antimicrobial properties and inhibited the growth of bacterial test strains used in this study.   Conclusion: The study demonstrated that nano Nickel oxide (NiO) particles could be successfully prepared using the hibiscus aqueous plant extract. The NiO-NP exhibited antimicrobial property against pathogenic E. coli and S. aureus bacteria, indicating that it could be used in formulations for treating infections by these organisms.