Fast lithium ion conducting glass-ceramics were successfully prepared by heat-treatment of glasses in the system Li2O-Al2O3-GeO2-P2O5. The phase present in the glass-ceramics was LiGe2(PO4)(3) in which Ge4+ ions were partially replaced by Al3+ ions. Composition dependence of conductivity showed that substitution of Al3+ ions for Ge4+ ions resulted in a considerable enhancement in conductivity and in a wide composition range extremely high conductivity over 10(-4) S cm(-1) was obtained at room temperature.