The biosorption of Reactive Orange 16 by Gracilaria verrucosa was evaluated under several parameter conditions. The biosorption method consisted of adding 0.2 g G.verrucosa biomass in 50 ml of dye solution concentrations (10-1000 mg/L) together in an orbital rotary shaker. The biosorption profile was highly dependent upon the initial pH concentration,  temperature, the adsorbent dosage and size. G.verrucosa biomass exhibited higher uptakes at pH 4 of all concentrations examined. The high uptake values of 0.2 g/50 mLwas observed and then decreased for the further increase in dosage.As the temperature increased the uptake of dye increases up to room temperature and the uptake decreases with further increase in temperature. As the size increased the uptake of dye increased up to 0.5mm and the uptake decreases with further increase in size. Therefore size was taken as 0.5mm/50mL, for biosorption experiments.Biosorption isotherms have been correctly represented by Langmuir and Freundlich non linear isotherm model. Biosorption isotherm data fitted better into Langmuir model.

KEYWORDS: Reactive dye, De-colorization, Reactive Orange 16, isotherm, Red seaweed, Macroalga