Adsorption isotherms were determined at 0 ℃ for carbon monoxide on type CuHY and type CuNaY zeolites which have various cupric ion contents. Adsorption of carbon monoxide on NaY and HY obeyed the Henry's law at low pressures. As the sodium ions on NaY and the protons on HY were replaced by the cupric ions, the adsorption characteristics were changed to follow Freundlich equation at relatively lower level of cupric ion exchange. In case when the cupric ion exchange level increased further, the Freundlich plot showed two or three distinct segments of linear nature with different slopes. In view of cremer's explanation method and Freundlich equation for adsorption on heterogeneous surfaces, it may be concluded that, at higher level of cupric ion exchange, cupric ion can be exchanged even in the supercage on HY while it cannot on NaY and that the cupric ion exchanged in sodalite unit appears to have influences on the adsorption of carbon monoxide in supercage for CuNaY and CuHY. The influence was more pronounced for CuHY than for CuNaY.