Ion-Exchange equilibria of alkaline earth metal ions (M = Mg2+, Ca2+, Sr2+, and Ba2+) /H+systems was studied on tin(IV) antimonate (SnSbA) in [M(NO3)2-HNO3] media at 30, 45, and 60°C. The ion-exchange isotherms showed sigmoidal curves without hysteresis effect for each ion-exchange system. The plots of the logarithm of the selectivity coefficient (In Kc) vs. equilibrium fraction (X¯M) of alkaline earth metal ion in the exchanger could well be described by two straight lines which intersect at about X¯M= 0.2. The slope of the straight line at X¯M< 0.2 increased in the order Mg2+< Ca2+< Sr2+< Ba2+. Overall and hypothetical (zero loading) thermodynamic data were evaluated from the plots. The selectivity sequence on (zero loading) was Mg2+< Ca2+< Sr2+< Ba2+while the overall affinity sequence was Sr2+< Ba2+< Ca2+< Mg2+.