The contamination of water by organic pollutant viz. phenolic compounds is a worldwide environmental problem due to their highly toxic nature. Surface modified zeolite materials have been developed from a waste material like fly ash which are being used for adsorption of phenol and o-chlorophenol from wastewater. The comparison of adsorption of phenol and o-chlorophenol on commercial zeolite-Y, fly ash based zeolite (FAZ-Y) and surface modified fly ash based zeolite (SMZ-Y) were studied. It was observed that the adsorption of phenol on SMZ-Y was 4.05 and 3.24 times higher than the FAZ-Y and commercial zeolite-Y, respectively. For o-chlorophenol the efficiency is higher by a factor of 2.29 and 1.8 for FAZ-Y and commercial zeolite-Y, respectively. This may be attributed to the hydrophobicity imparted by surfactant molecules on the surface of fly ash zeolite, consequently leading to organic partitioning. The effect of various parameters like adsorbent dose, pH and initial concentration were studied for their optimization. The rate of adsorption of phenol and o-chlorophenol was found to be maximum at neutral pH. The effect of the presence of anions on adsorption of solute was also studied. It was found that the salts have a substantially detrimental effect on adsorption of phenol and o-chlorophenol. Equilibrium adsorption data for phenol and o-chlorophenol were analyzed by using Freundlich adsorption isotherms model. (C) 2007 Elsevier B.V. All rights reserved.