Ion exchange properties of pure potassium-based geopolymer (pure K-GP) formulated with Si/Al=2.1 and K/Al=1.0+/-0.02 atomic ratios have been studied. For pure K-GP, the maximum ion-exchange level of K + with respect to Na + and Cs + is 77 and 61%, respectively, as determined by exhausted exchange with 1M solutions of appropriate nitrates at 22+/-2 o C. The geopolymer shows a slight preference for K + over Cs + as indicated by the normalized Cs/K-GP isotherm obtained under noncompetitive exchange. Parent geopolymer yields a pure geopolymer when it is extensively washed with deionized water until neutral pH is obtained and equilibrated with aqueous solution of KNO 3 resulting in changing in composition and textural properties. As calculated from N 2 sorption-desorption isotherms, surface specific area and cumulative pore volume for parent K-GP are 5.5m 2 g - 1 and 0.01cm 3 g - 1 , respectively, whereas for pure K-GP surface specific area and cumulative pore volume are 270m 2 g - 1 and 0.4cm 3 g - 1 , respectively.