The separation of 90Y from 90Sr was carried out by ethanol‐ and methanol‐water systems from NH4‐form Dowex 50‐X4 columns. Maximum fractions of radiocolloidal 90Y was eluted by using 50% solvent solutions. Using 20, 50, and 80% aqueous ethanol as solvent, the eluted activities were 2, 18 and 13% respectively, and with 20, 50 and 80% aqueous methanol, the activities were 2, 7, and 4% respectively. Fractional conversion of ionic yttrium to radiocolloids was observed and the anormal adsorption of radiocolloids in the column was thought to be due to the growing agglomerates retained in the canals in the resin beads.