Zeolites are used as adsorbents of cationic elements in the radioactive decontamination process of water, soil and others. We determined Cs+ and Sr2+ adsorption selectivity of some zeolites to know effective zeolite species for the decontamination of radioactive Cs and Sr. A 30 mL mixed solution containing up to 15 mg L−1 of non-radioactive Cs+ or Sr+ and up to 0.50 M of Na+ or K+ was mixed with 0.5 g of Linde-type A, Na-P1, faujasite X, faujasite Y and mordenite. Among the zeolites, mordenite had the highest Cs+ adsorption selectivity, and the selectivity had no correlation to the cation exchange capacity (CEC) of the zeolites. In contrast, Sr2+ adsorption selectivity of the zeolites positively correlated with the CEC of the zeolites; Linde-type A with the highest CEC showed the highest adsorption selectivity, and its adsorption rate was more than 99.9% even in the presence of 0.5 M K+. A simulated soil decontamination experiment of Cs from a Cs-retaining vermiculite by using mordenite and that of Sr from a Sr-retaining vermiculite by using Linde-type A showed decontamination rates of more than 90%.