The uptake of various cations by imperfectly ordered KAISiO_4 was investigated. The KAISiO_4 was prepared by solid-state reaction of kaolinite with K_2CO_3 at 550℃ for 24h. Uptake experiments were performed at 60℃ using 0.5g of the KAISiO_4 and 50 ml of solution containing 10^<-3>-10^<-1> M of each cation, with and without 0.5 M NaCl buffer. The cations were alkali 8Li^+ and Na^+), alkaline earth (Mg^<2+> Ca^<2+> Sr^<2+> and Ba^<2+>) and transition metal cations (Ni^<2+> Co^<2+> Cu^<2+> and Zn^<2+>). From the comparison of uptakes of various cations by KAISiO_4 and zeolite Na-A, it was found that the ratio of uptake by both exchange materials increased with decreasing ionic radius of the exchanging cations, the KAISiO_4 showing higher uptake of Ni^<2+> than zeolite Na_A. This trend became more distinct for the uptake of Ni^<2+> in simulated acid waste solution and ground-water because of the suppressing effects by co-existing alkali and alkaline earth cations especially for zeolite Na-A.