The release of dye containing effluent is a great threat to the environment today. The Loss of dye within textile wastewaters could vary from 5% for basic dyes to as high as 50% for reactive dyes, leading to severe contamination of surface and groundwater. The purpose of this study is to optimize dye decolorization and COD removal of reactive red dye from aqueous solution via green synthesized iron nanoparticles. Nowadays, green synthesis methods have gained growing attention in nanotechnology owning to their versatile features including high efficiency, cost-effectiveness, and eco-friendliness use in environmental application. Here, the aqueous extract of Eucalyptus leaf was applied for the preparation of iron nanoparticles (Fe-NPs) which were used as a catalyst in Fenton oxidation of Reactive red Azo dye. The synthesized iron nanoparticle catalyst was characterized to know its functional groups presents, morphology, surface area, and the particle size by FTIR, SEM, XRD, and DLS instruments. The synthesized iron nanoparticles were confirmed by the absorption peak at 357nm with an average size of 61.79nm. The result shows spherical shape and surrounded by a layer of biological compounds and the structure were dominated by amorphous nature. The CCD based on response surface methodology was applied to determine the interactive effects of the process parameters and their optimum conditions. Batch experiments revealed that the adsorption kinetics followed a pseudo-second order rate model whereas adsorption isotherm was best fitted to the Langmuir model (R2=0.999) with qm = 71.94 mg g-1 and the adsorption of RRD on iron nanoparticles is endothermic and spontaneous in the temperature range (298-323K). In Fenton like process the degradation of Azo dye were studied over a wide range of initial dye concentration (25-75mg/l), catalyst load (1-1.6g/l) and the dose of H2O2 (2-6mM/l) constant pH 3, contact time of 120min and room temperature. The maximum dye decolorization and COD removal percentage were 95.4% and 74% respectively, under the dosages of 1 g/l of iron nanoparticle catalyst, 4mM/l of H2O2 and 25mg/l of dye concentration. Nanoparticles can exhibit unique catalytic properties due to their size and surface characteristics, leading to higher reaction rates and heterogeneous Fenton can be applied to treat a wide range of contaminants under various conditions, making it a versatile approach for environmental cleanup. Key words: Azo dye, Fenton oxidation, Hydrogen peroxide, Iron nanoparticle