The binding of strontium by humic acid was studied in systems designed to model soil leaching conditions. Ultrafiltration experiments were conducted for a wide range of CaCl and NaCl concentrations and for the pH range 4 to 7. It was found that the recovery of humic acid slowly decreased with increasing pH. This occurred because at neutral and basic solutions the increasing degree of ionization of the carboxylate groups leads to the full repulsion state of the humic acid and to increasing of the strontium binding (strontium recovery 60% at pH 7) with this natural polyelectrolyte. The strontium complexation in the presence of calcium was studied in different series of metal concentrations at pH 5 and the ionic strength 0.1M NaCl. The results were explained on the base of the metal ion charge neutralization model of humic complexation (CNM). Loading capacity (cca 40%) and complexation constants and Sr (3.51±0.27) and Ca (3.10±0.29) with Aldrich humic acid were found.