In this work, the ability of surface modified zeolite (SMZ), obtained by ion exchange of phillipsite-rich tuff with HDTMA (hexadecyltrimethylamm onium)-Br or HDTMA-Cl, to adsorb amoxicillin was investigated. The effect of surfactant modification was explored by contacting the tuff with HDTMA solutions at different concentrations (50-200% of the zeolite's external cation exchange capacity). It was found that for the higher surfactant concentration used the formation of a surfactant bilayer (compact for HDTMA-Br, patchy HDTMA-Cl) occurs. The results of the adsorption experiments showed that SMZ exhibited a higher adsorption capacity (especially at low solute concentrations) and a faster adsorption rate for amoxicillin than the unmodified tuff. The interaction between amoxicillin and the adsorbents was mainly ascribed to electrostatic forces.