The three natural zeolites collected in Yungil-gun, Kyungsangbuk-do, Korea, were analyzed by means of chemical wet methods and X-ray diffraction. The results indicated that the primary species of those zeolites were clinoptilolite mixed with heulandite, feldspar, montmorillonite, and quartz. These zeolites were chemically treated with NaOH, Ca(OH)_2, and HCl solution and their differences were also studied with X-ray diffraction method. The capabilities of removing Cs^+ and Sr^2+ ions with chemically untreated zeolites, chemically treated zeolites, and also with synthetic zeolites were compared. The effect of other cations in removing Sr^2+ ions was also studied. The experimental results showed that Cs+ and Sr^2+ ions could be removed up to 98% and 95% respectively out of 5 ppm with chemically untrearted natural zeolites. The treatment of 0.02N-Ca(OH)_2 and that of 2N-NaOH were most effective in removing Cs^+ and Sr^2+ ions, respectively. It was found that the mountaintop of Sangjung 1-dong natural zeolite treated with 2N-NaOH was most efficient in removing Sr^2+ ions mixed with other cations, compared with any other chemically treated and untreated natural zeolites in this work.