Speciation of Eu(III) in the presence of purified Aldrich humic acid (PAHA) and/or aluminum oxide α-Al 2 O 3 has been studied by batch experiments and time-resolved luminescence spectroscopy at different pH, ionic strengths and PAHA concentrations. Macroscopic and spectroscopic data (sorption, spectra, and decay times analyses) are compared between the ternary system, i.e., Eu(III)/PAHA/α-Al 2 O 3 , and the corresponding binary systems. As expected, results show a weak influence of ionic strength on Eu(III) adsorption onto α-Al 2 O 3. However, in the binary Eu(III)/PAHA system, it is evidenced that variations of electrolyte concentration, which modify PAHA conformation, influence the symmetry of the humic-bound Eu(III) at high pH. In the ternary system, adsorption of both Eu(III) and PAHA onto the surface decreases with ionic strength. At 0.01 mol/L NaClO 4 , Eu(III) luminescence decay is much faster than at 0.1 mol/L NaClO 4. This is most likely due to the lower surface concentration of PAHA at lower ionic strength, leading to a lesser constrained environment for Eu(III) ions. At high pH, luminescence spectra are different at the two ionic strengths studied. Concerning the influence of PAHA concentration, spectroscopic results show that in the binary Eu(III)/PAHA system a complete complexation of 1 µmol/L Eu(III) is reached for 16 mg/L PAHA at pH 4, and for lower PAHA concentrations at higher pH. At same PAHA concentration, there is no difference in asymmetry ratios between the binary Eu(III)/PAHA system and the ternary system between pH 4 and 7.7. This means that the presence of mineral surface has almost no influence on Eu(III) environment symmetry below pH 8. Hence, the occurrence of europium-bridged humic surface complexes is not likely. In the ternary system, at different pH, luminescence decay times of Eu(III) increase with PAHA concentration. They are much higher in the ternary system than in the binary Eu(III)/PAHA system, which would mean that Eu(III) environment in PAHA-bound molecules is more constrained, as previously seen [1]. Macroscopic results show that the influence of PAHA on Eu(III) sorption onto α-Al 2 O 3 depends on pH: at low pH, Eu(III) retention is always higher in the ternary system, whereas at higher pH it depends on PAHA concentration. [1] N. Janot, M. F. Benedetti, P. E. Reiller, Environ. Sci. Technol. 2011, 45, 3224.