Potential of Kappaphycus alvarezii, low cost marine seaweed has been studied for adsorption of azo dye from aqueous solution. Batch mode adsorption experiments were performed to remove anionic dye Congo red under various experimental conditions. It was found that the extent of Congo red adsorption by red weed biomass increased with initial dye concentration, contact time, initial solution pH and quantity of adsorbent. The adsorption process was pH dependent and the maximum adsorption of 45 mg/g occurred at pH of 8 for an initial dye concentration of 50 ppm by K. alvarezii. Adsorption isotherms and kinetic models were applied in the adsorption process. Equilibrium data were best represented by Langmuir isotherm model, which implies the monolayer adsorption of dye molecules on the adsorbent. Langmuir constant ‘KL’also indicated the favourable adsorption. Overall, kinetic studies showed that the dye adsorption process followed the pseudo-first-order kinetics. The present investigation reveals that the dry biomass of red seaweed can be an economical alternative adsorbent for the treatment Congo Red from aqueous solution.