Our current study deals with the green synthesis of copper nanoparticles using extract of Labeo rohita fish scales. There is no need to add any external reducing and stabilizing agents as the gelatin found in fish scale extract possesses plenty of reducing and stabilizing properties. The synthesized copper nanoparticles (Cu-NPs) were characterized by Zeita sizer and SEM. Cu-NPs were applied to decolorize Reactive Blue 19 dye. Different experimental conditions like concentration of reactive Blue 19 dye, concentration of copper nanoparticles, pH and temperature were optimized. The degrading potential of copper nanoparticles increased their applicability for the decolorization of Reactive Blue 19 dye. Reactive Blue 19 dye was maximum decolorized (90.18%) at aconc. of 0.03%, 4 mg Cu-NPs, pH 10 at 50ºC. The effectiveness of the method was evaluated by water quality assurance parameters such as total organic carbon (TOC) and chemical oxygen demand (COD). The reaction products were characterized by FTIR spectral studies.