Alginate bead is a promising adsorbent for Sr ions in solution, but their adsorption performance is limited in seawater due to the competition with other concentrated ions. In this study, MnO2-alginate beads were prepared by immobilizing MnO2 in alginate, and their feasibility for Sr adsorption in seawater was evaluated. MnO2-alginate beads consisted of 16.1% MnO2 and 7.0% alginate, while plain alginate beads contained only 3.7% alginate. That is, immobilizing MnO2 in alginate induced a compact structure in the MnO2-alginate beads, which resulted in a lower amount of moisture. Sr adsorption on MnO2-alginate beads occurred predominantly on the alginate part and partially on the MnO2. Compared with plain alginate beads, MnO2-alginate beads exhibited significantly improved Sr adsorption efficiency in the presence of seawater with a concentration of Na (10,000 ppm), Mg (1200 ppm), Ca (400 ppm) and K (400 ppm) due to its enhanced Sr selectivity against Na and increased number of Sr adsorption sites. Finally, MnO2-alginate beads exhibited four times higher Sr adsorption efficiency than plain alginate beads in real seawater. These results demonstrate that MnO2-alginate beads are a highly feasible adsorbent for Sr removal from seawater. (C) 2017 Elsevier B.V. All rights reserved.