Lithium superion conductors, Li3+2x(Sc1-xMgx)(2)(PO4)(3), Li3-2x(Sc1-xMx)(2)(PO4)(3) (M=Ti, Zr, Sn, Hf) and Li3-4x(Sc1-xMx)(2)(PO4)(3) (M = Nb, Ta) were prepared by a solid-state reaction. TG-DTA analysis indicated no phase transition in Li3+2x(Sc1-xMgx)(2)(PO4)(3) and Li3-2x(Sc1-xMx)(2)(PO4)(2) (M = Ti, Zr, Sn, Kf) with x higher than 0.05, and in Li3-4x(Sc1-xMx)(2)(PO4)(3) (M=Nb, Ta) with x higher than 0.025. The room temperature ionic conductivity of Li3Sc2(PO4)(3) has been increased by three orders of magnitude with the highest conductivity observed in Li3-2x(Sc1-xTix)(2)(PO4)(3) with x = 0.20 and in Li3-2x(Sc1-xZrx)(2)(PO4)(3) with x = 0.10. It was ascribed to the stabilization of the high temperature superionic conduction phase and the introduction of vacancies on the Li+ sites by substituting Ti4+ Or Zr4+ for Sc3+.