Dyes are the main input as a coloring agent for textile and some other industries. When these wastewaters enter into nearby marine environment, it can harm marine species and pollute the whole freshwater ecosystem. So, treatment of these industrial effluents is necessary before discharging it to the environment. Currently, we have synthesis a non-toxic and biogenic CaO nanoparticle from the leaves of Murraya koenigii leaves. Then the nanoparticles were characterized using UV, FTIR, XRD, SEM and TEM. The UV data shows absorbance at 345 nm. While the obtained band gap was about 2.5 eV. Further, characterization tests confirmed the formation of CaO nanoparticles. CaO nanoparticles was applied for treatment of methyl red and methyl blue dyes solutions under UV light and without UV light in order to check its degradation capability. Methyl red degradation was slow as compared to methyl blue. The results obtained shows that, under UV light the synthesized nanoparticles fully degrade methyl blue in 20 minutes. Whereas, 70% methyl red was degraded in 60 minutes under UV light. While, without UV light the degradation was about 10% for methyl blue and 5% for methyl red respectively.