The isotope fractionation of Mo(VI) species using benzimidazole-type anion-exchange resins embedded in high-porous silica beads was investigated in various HCl solutions ranging in concentration from 0.1 to 11.2 M (M = mol/dm3) at 298 K. As a result, the plots of the slope coefficients of Mo(VI) species against the corresponding b values, which are parameter of the adsorbent–adsorbate relative affinity in the adsorption process, were found to be a good linear relationship and the isotope fractionation coefficients of Mo(VI) species were also obtained by using the isotope fractionation curve of Mo(VI) species.