This study manifests the simple, environmentally-friendly and inexpensive synthesis of small sized copper oxide nanoparticles (CuO NPs) using the aqueous extracts of Justicia carnea. The aqueous extracts of Justicia carnea serve as effective reducing and capping agents for the green-synthesized NPs. The reduction of CuII was visually observed by the change of colour from light green to brown with formation of precipitate. The reaction was followed by UV-Visible spectrophotometry and the characterization of the copper oxide nanoparticles by Fourier Transform Infrared spectrophotometery. The UV-Visible spectra of aqueous solutions containing the synthesized copper nanoparticles showed a maximum absorption peak at 240 nm corresponding to surface plasmon resonance (SPR) of copper oxide nanoparticles. The FTIR spectrum of CuO NPs shows peaks corresponding to bands associated to Cu-O stretching and bands which represent characteristic peaks believed to be due to the interaction of CuO with biomolecules of extract.