Four ZSM-5 zeolite catalysts with different Si/Al ratios for the catalytic cracking Of C-4 fractions to produce ethylene and propylene were prepared in this study. First, the adsorption isotherms of pure n-butane and butene-1 and their mixtures on these catalysts at 300K and p=0-100kPa were measured using the intelligent gravimetric analyzer. The experimental results indicate that the presence of Al can significantly affect the adsorption of butene-1 than that of n-butane on ZSM-5 zeolites. Then, the double Langmuir (DL) model was applied to study the pure gas adsorption on ZSM-5 zeolites for pure n-butane and butene-1. By combining the DL model with the ideal adsorbed solution theory (IAST), the IAST-DL model was applied to model the butene-1 (1)/n-butane (2) binary mixture adsorption on ZSM-5 zeolites with different Si/Al ratios. The calculated results are in good agreement with the experimental data, indicating that the IAST-DL model is effective for the present systems. Finally, the adsorption over a wide range of variables was predicted at low pressure and 300K by the model proposed. It is found that the selectivity of butene-1 over n-butane increases linearly with the decrease of Si/Al ratio. A correlation between the selectivity and Si/Al ratio of the sample was proposed at 300K and p=0.08MPa.