A Mexican clinoptilolite-rich tuff was modified with the hexadecyltrimethyl ammonium (HDTMA) and used for the sorption of phenol and 4-chlorophenol. Whereas the zeolitic tuff had no affinity for phenol and 4-chlorophenol, the modified zeolite removed these organic compounds. The sorption behavior from aqueous solutions was studied by means of batch type and column experiments and isotherms were determined. It was found that the uptake was higher for 4-chlorophenol than for phenol.