Graphene oxide (GO) supported iron molybdate (Fe₂(MoO₄)₃) was prepared via hydrothermal route, which were characterized by X-rays diffraction technique (XRD), scanning electron microscopy (SEM), Energy-Dispersive X-Ray (EDX), zeta sizer, UV–visible and atomic force microscopy (AFM) techniques. Photocatalytic activity (PCA) was evaluated by degrading the diclofenac sodium (DS) under solar light irradiation. Central composite design (CCD) was employed under response surface methodology (RSM) for the optimization of process variables such as pH, H₂O₂, DS concentration and catalyst load for maximum drug degradation. At optimum conditions, up to 96% DS degradation was achieved (2 h irradiation, 6% H₂O₂ concentration, 10 mg/L DS concentration, 0.45 g/L catalyst dose and 4.5 pH). The statistical analysis revealed the adequacy of developed model for the degradation of DS drug. The actual and predicted degradation values correlated well with each other with very low residual value. The model fitness was based on insignificant “lack of fit test” and higher value R². Results revealed that the hydrothermal route is an efficient route for the fabrication of GO/Fe₂(MoO₄)₃ round-ball microstructures, which showed promising PCA and it could possibly be used for the degradation of DS drug in wastewater.