The current research is designed to synthesis Copper oxide nanoparticles (CuO NPs) using Cyanobacterium in greener way. The NPs were synthesized using Spirulina platensis. The method is adopted for the less toxic, less cost and environment friendly method. The synthesized CuO NPs are capped and stabilized by the natural substance of S. platensis including flavonoids, phenolic and acid groups of the microorganism which was confirmed by the GC-MS analysis. Majorly, beta-ionone, p-cumic aldehyde, phytol compounds are identified by GC-MS and it may also involve in the preparation of NPs. Further, the characterization has been carried out using UV–Vis spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction, Scanning electron microscope (SEM), transmission electron microscope (TEM). All the analytical techniques are confirmed the formation of NPs. The formed NPs are showed significant peaks in XRD analysis which further compared with literature. Functional group analysis showed –OH group compounds in extract and it might involve in the formation of NPs. The photo catalytic activity of CuO NPs was showed significant photo degradation of Congo red (CR) dye. The consideration of intense peak, the size of CuO NPs was calculated and found to be 15.2 nm with spherical shape as resulted in morphological identification. The results are showed good photocatalytic activity, since the peak appeared at 230 and 495 nm corresponding to the benzene and azo group of Congo Red were gradually decreased with increase of time. The reaction was found to have nature of pseudo first order reaction. The rate constant was calculated and was found to be - k = 0.3459, which indicates the Congo red degradation was 0.3459 per minute. This study will be a base for budding researchers for their isolation of S. platensis active compounds and with the help of secondary metabolites (active compounds) CuO NPs were synthesized which further acted has degradation agent against Congo red.