The quantitative relationships between enhancement of magnetization intensity and structural water content in hydrated β''- and β'''-ferrites were studied. The Cd-stabilized Na-β''-ferrite, whose maximun structural water is 3.7 mol/f.u., showed the highest enhancement of the magnetization intensity up to 28.4μWb·m/kg, while the magnetization intensity of K-β''-ferrites was enhanced little by any hydration conditions. It is clear that enhancement of the magnetization intensity of β''-ferrites is directly proportional to the structural water content over 1.5 mol/f.u. in the ion-conductive layer. Enhancement of the magnetization intensity of β'''-ferrites, however, is independent of the structural water content.