||The use of cesium is increasing in the medical and industrial field, and as a result, a large amount of cesium is found in wastewater. Cesium is harmful to health because it induces toxicity. Prussian blue (PB) acts as an effective absorber to remove cesium ions. But it is difficult to reuse by filtering because of the microcrystalline structure. For efficient use of PB, sodium alginate can be used as a matrix of PB. sodium alginate is linear copolymer including blocks of (1,4)-linked-β-D-mannuronate(M) and α-L-guluronate(G) residues. Alginate hydrogels are formed by cross-liking with adding certain divalent and trivalent metal ions in G block. In this study, alginate hydrogel was cross-liked by trivalent iron ions. PB was grown by addition of the solution of hexacyanoferrate ions to alginate hydrogel at the site where the sodium of sodium alginate was replaced by a trivalent iron ion. Sodium alginate was mixed with a polymer to overcome the fault before alginate formed a hydrogel.