The ion exchange equilibria of Cr(NH3)3+, Cr(NH3)5Cl2+, cis-Cr(en)2Cl2+, trans-Cr(en)2(SCN)2+, Cr(H2O)63+complex ions against La3+ions were studied. The effect of the ionic charge, radius and composition of various chromium complex ions on the selectivity were discussed. The logarithms of the selectivity constants were plotted versus mole fraction of complex ions in the resin phase. Linear variations with negative slopes were observed in experiments except for the Cr(H2O)63+-La3+system.