Pure and binary adsorption isotherms of propylene and ethylene on silicalite-1 were determined using the intelligent gravimetric method. The ideal adsorbed solution (IAS) theory and the extended Langmuir (EL) model were used to predict binary adsorption isotherms from the adsorption isotherms of the pure components. At higher molar fraction of propylene in the gas phase, the results predicted by both the IAS theory and the EL model are in good agreement with the experimental data, but at low molar fraction of propylene in the gas phase, the predicted results deviate from the experimental data evidently. (C) 2004 Elsevier B.V. All rights reserved.