Researchers are interested in green technology because it is a low-risk, eco-friendly and affordable way to biosynthesize nanoparticles (NPs). Copper nitrate trihydrate and Nigella sativa extract were used as a reducing and capping agent during the manufacture of copper oxide (CuO) NPs in this investigation. The biosynthesized CuO NPs were characterized using X-ray diffractometer, transmission electron microscopy, UV–Vis spectroscopy, scanning electron microscopy and Fourier transform infrared (FTIR) spectroscopy. The good crystalline nature perfectly matches the monoclinic structure of bulk CuO. The results obtained from TEM also showed that CuO NPs were semi-spherical in shape, while the zeta potential characterization indicated that the prepared particles have low stability. Moreover, CuO NPs showed good antimicrobial activity.