This study reports the biosorption of MG using a novel nano zero valent iron Sargassum swartzii (nZVI-SS) biocomposite. Response surface methodology derived from Box-Behnken design (BBD) was applied for optimizing the essential variables such as pH, initial MG concentration, and biosorbent dosage. The results obtained from BBD design showed the maximum biosorption capacity of 73.5mg/g at pH 10, initial MG concentration of 100mg/L, and biosorbent dosage of 0.55g/L. The biosorption was highly dependent on pH and initial dye concentration. The nZVI-SS biocomposite was characterized using SEM, FTIR, TGA, and DSC analysis. The experimental and analytical result shows that nZVI-SS biocomposite can be effectively used as prominent biosorbent for the removal of dye bearing wastewater.