The trivalent ionic conduction in the Sc-2(WO4)(3)-Lu-2(WO4)(3) solid solution, which possesses the Sc-2(WO4)(3)-type structure was investigated. The Sc site substitution in Sc-2(WO4)(3) for larger Lu3+ occurred completely and the cell volume of the solid solution linearly expanded with increasing the Lu content. The ionic conductivity of the solid solution system enhanced with increasing the Lu substitution of the Sc site in Sc-2(WO4)(3) up to 50 mol%. On the other hand, the conductivity decreased by replacing the Lu site in Lu-2(WO4)(3) for Sc3+ UP to 40 mol%. A discontinuity appeared in the relation between the ionic conductivity and the composition of the solid solution around 50-60 Lu mol% substitution of the Sc site in the Sc-2(WO4)(3)-type structure. The electrolysis results derive the conclusion that the solid solution is a Sc3+ and Lu3+ trivalent mixed conductor and the mainly conducting species is Sc3+ and Lu3+ below and above 50-60 Lu mol%, respectively.