The present study investigated the potential of Ulva lactuca in dye decolorization and degradation. The optimum tolerance concentration of biomass was observed under lower concentrations of azo dye. The degradation potential of biomass was studied by FTIR (Fourier-transform infrared spectroscopy) analysis of azo dye for pre and post treatment. The biochemical response of the biomass by analysis of chlorophyll-a, chlorophyll-b, total chlorophyll and carotenoid, total soluble sugar and protein was observed decreased with increasing days and dye concentration. The surface characteristic of the biomass was studied by SEM (Scanning electron microscopy). The experimental results indicate the order of decolorization as reactive red-195 > reactive yellow -145 > reactive black -5. Thus, Ulva lactuca shows significant decolorization and degradation.