The present research work primarily deals with the characterization and antimicrobial efficacy of aluminium oxide, iron oxide, copper oxide and zinc oxide nanoparticles synthesized by a coprecipitation method. The prepared nanoparticles were characterized by XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Radiation), UV-Visible spectroscopy and SEM (Scanning Electron Microscope) with EDX (Energy Dispersive X-ray analysis). The antibacterial activity and minimum inhibitory concentration of the nanoparticles were carried out by agar well diffusion method and broth dilution method respectively against gram negative (Escherichia coli and Proteus vulgaris) and gram positive (Staphylococcus aureus and Streptococcus mutans) bacteria. The average crystallite size of the metal oxide nanoparticles was found to be 35nm (Al2O3, IO, ZnO ) and 19nm (CuO) by X-ray diffraction. The antibacterial activity test evidently expressed that gram negative bacteria are much sensitive to metal oxide nanoparticles when compared to gram positive bacteria. The results suggest that the synthesized metal oxide nanoparticles (Al2O3, CuO, Fe3O4, and ZnO) are effective antimicrobial agents.