The sorption of Eu species onto nano-size silica-water interfaces is investigated at pH range of 1―8.5 and the initial Eu concentrations (CEu) of 2 × 10-5, 2 × 10-4 and 2 × 10-3 M using fluorescence spectroscopy. The sorption rate of Eu is initially low, but significantly increases at pH > 4. For the initial CEu of 2 × 10-5, 2 × 10-4 and 2 × 10-3 M, the dissolved Eu species are completely sorbed onto silica-water interfaces at pH = 4.75, ～5.8 and 6.6, respectively, with the respective sorption densities of ～1.58 × 10-8, 1.58 × 10-7 and 1.58 × 10-6 mol/m2. The sorbed Eu species at pH < 6 is aquo Eu3+, which is sorbed onto silica-water interfaces as an outer-sphere complex at pH < 5, but may be sorbed as an inner-sphere bidentate complex at 5 < pH < 6, due to the decrease of the NH2O to ～6 at pH = 6. At pH = 6 - 8, Eu(OH)2+, Eu(CO3)+ and Eu(CO3)2- form in the solutions, and Eu(CO3)+ is dominant at pH = ～7.5. These ions may be sorbed onto silica-water interfaces as inner-sphere bidentate complexes or multi-nuclear precipitates.