Cobalt oxide nanoparticles were prepared by eco-friendly Co-precipitation method using Cobalt Sulphate heptahydrate as precursor and sodium hydroxide as a stabilizing agent. The prepared nanoparticles were characterized by various techniques thermal analysis (TGA), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transformer Infrared spectroscopy (FTIR), Energy dispersive X-ray analysis (EDXA) and UV-Visible spectroscopy. Optical properties showed an energy band gap i.e. direct and indirect band gap as 1.87 eV and 1.72 eV. The average particle size of cobalt oxide nanoparticles was found to be 25 nm from XRD.