Caulerpa racemosa var. cylindracea is one of the well-known invasive species in the Mediterranean Sea. In the present study, dried biomass of C racemosa var. cylindracea was shown to have adsorption capacity for methylene blue. The adsorption reached equilibrium at 90 min for all studied concentrations (5-100 mg/L). The pseudo-second-order model is well in line with our experimental results. There was a sharp increase in the adsorbed dye amount per adsorbent amount from 3.3 to 16.7 g/L, then a slight increase up to 66.7 g/L was observed. Langmuir and Freundlich's models were applied to the data related to adsorption isotherm. According to Langmuir's model data, the observed maximum adsorption capacity (q(m)) was 5.23 mg/g at 18 degrees C. The enthalpy of adsorption was found to be 33 kJ/mol, which indicated a chemical adsorption between dye molecules and C. racemosa var. cylindracea functional groups. (c) 2007 Elsevier Ltd. All rights reserved.