A new trivalent cation conducting solid electrolyte with the NASICON-type structure, Sc1/3Zr2(PO4)(3), was synthesized by a sol-gel method and trivalent cation conducting properties were investigated. The trivalent ion conductivity of Sc1/3Zr2(PO4)(3) was comparable to those of the trivalent ion conducting tungstates with the Sc-2(WO4)(3)-type structure and its conductivity at 600 degreesC is 1.06x10(-4) S cm(-1), which is 2.5 times as high as that of Al-2(WO4)(3). The Sc3+ cation migration in Sc1/3Zr2(PO4)(3) was directly demonstrated by a de electrolysis.