Abstract: Liquid adsorption in fixed bed was studied at room temperature for the binary system, para-xylene and ethylbenzene, with two types of zeolites- one prepared by our group, and the other imported. The mathematical model included a mass transfer equation involving the total mass transfer coefficient, and the equilibrium and the mass balance equations. These three equations were integrated numerically. The predicted breakthrough curves was close to the experimental. To explore further the mechanism of mass transfer, three models-liquid-phase controlling, solid-phase controlling and both-phase controlling were examined. The results showed that the solid-phase controlling model is the most appropriate for a system studied.