Activated carbon (AC) prepared from marine algae was found to be a potential adsorbent for Congo red dye for removal from aqueous solution. The AC was prepared from marine algae Valoria bryopsis by treatment with conc. H2SO4. The surface area of the AC and its properties were studied by scanning electron microscopy (SEM). Adsorptive removal of Congo red from aqueous solution onto AC has been studied under varying conditions of agitation time, metal ion concentration, adsorbent dose and pH to assess the kinetic and equilibrium parameters. Adsorption equilibrium was found to be reached in 180 min for 5 to 25 mg/L of Congo red concentrations. The Langmuir and Freundlich isotherm models were found to provide an excellent fitting of the adsorption data. For the Freundlich isotherm, high r2 values were obtained (0.8460 to 0.6992) for Congo red concentration of 10 to 60mg/L, which indicated favorable adsorption of Congo red onto marine algae carbon. The adsorption capacity of Congo red was found to be 97.77%. The percent removal increased with increase in pH from 1 to 5. This adsorbent was found to be effective and economically attractive.