This paper presents a green synthesis of plant modified copper oxide nanoparticles (CuO NPs) using Justicia adhatoda L. (J. adhatoda) aqueous leaves extract. The nano particles of CuO were synthesized by using CuCl2.2H2O and Justicia adhatoda L. aqueous leaves extract of various concentrations (1% - 5%) with simultaneous addition of NaOH at 80oC. The synthesized CuO NPs were studied by XRD (X-ray diffraction)), Ultra violet- Diffuse reflectance spectroscopy (UV-DRS), Fourier transform infrared spectroscopy (FT-IR). The morphology of sample was studied by Scanning electron microscopy (SEM) and High-resolution transmission electron microscopy (HR-TEM).