Copper oxide nanoparticles were synthesized using black tea extract and copper nitrate as the copper source by the green method at different calcination temperatures. This method has many advantages such as nontoxic, economic viability, ease to scale up, less time consuming and environmental friendly approach for the synthesis of CuO nanoparticles without using any organic chemicals. The synthesized CuO nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The average crystallite size of CuO nanoparticles was calculated using Scherrer formula. The Xray powder diffraction (XRD) analysis revealed the formation of monoclinic phase CuO with average particle size of 22-39 nm
