The specific adsorption of alkali ions, Li*, Ma*, and Cs*, in electrolyte solutions on Prussian blue (PB) is investigated by using the three-dimensional (3D) reference interaction site-model (RISM) theory. The results from 3D-RISM show dramatically different adsorption sites between large ions or and Cs+) and small ions (Li+ and Na+). The small ions are adsorbed at the channel entrance sites without the water ion exchange mechanism. In contrast, the large ions are adsorbed in PB by the water-ion exchange mechanism, and the adsorption site of large ions is located at the center of the cage or at the interstitial site. (C) 2017 Elsevier B.V. All rights reserved.