Softchemical synthesis of a new type of intercalation ionic conductor was attempted by intercalating Ag into precedently I-intercalated Sr1.5Bi7.5O12.75 whose pristine host is a typical van der Waals type of layered compound. As a result, a new layered Bi-based intercalation compound, Ag-I intercalated Sr1.5Bi7.5O12.75, was successfully synthesized, in which the guest atoms had been considered to be located in the van der Waals spacings of the pristine host. The conductivities of the new intercalation compound thus synthesized were of the order of 10(-4) (S/cm) at 500 K. The values were about 10(3)-10(4) times as high as, those of host and I-Sr1.5Bi7.5O12.75 without the intercalation of Ag. From the enhanced conduction properties in the Ag-I intercalated Sr1.5Bi7.5O12.75, migration of the Ag intercalated was suggested. The chemical composition in the guest layers, was varied with the added amount of Ag to starting mixtures, being in ranges from 0.68 to 0.76 for Ag and from 1.45 to 1.65 for I, respectively. In this report, the effects of guest composition on the structures and the conduction properties of Ag-I intercalated Sr1.5Bi7.5O12.75 were discussed.