The extract of seeds (Coiandrum Sativum) was used to prepare Cobalt oxide nanoparticles by green synthesis in an aqueous medium. The main advantage of using "Coiandrum Sativum seeds" as a stabilizer agent in the extract is that it gives nanoparticles long-term stability by avoiding particle aggregation. The particles have been examined using X-ray diffraction (XRD), energy dispersive (X-ray) analysis, transmission electron microscope (TEM), scanning electron microscopy (SEM), and (EADX). The image of TEM shows that the CoO-NPs have an average particle size of 28 nm, which agrees well with the XRD readings. The chemical spray pyrolysis method proved successful in producing Cobalt oxide thinfilm. X-ray Diffraction (XRD) analysis of the Cobalt oxide phase demonstrated that the Cobalt oxide phase was prepared. Atomic force microscopy (AFM) photographs of the topography of the film with grains smaller than 100 nm were used to describe the surface morphology. Cobalt oxide thin films that have been deposited and then annealed at 400 °C have a flat, smooth texture, making them perfect for optoelectronic applications.