Lithium ion conducting glass ceramics composed of the crystalline conductive phase Li1.4Al0.4(Ge1 - x.)(1.6)(PO4)(3)(X= 0-1.0) with the Nasicon-type structure have been synthesized and characterized by DTA, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and complex impedance techniques. The experimental results indicated that the glass ceramics were mainly composed of solid solution Li(Ge1 - xTix)(2)(PO4)(3) formed by LiGe2(PO4)(3) and LiTi2(PO4)(3) in the whole x range and showed conductivity over 10(-4)S/cm at room temperature. The maximum room temperature lithium ion conductivity of 6.21 X 10(-4) S/cm with an activation energy as low as 0.32 eV was obtained for the Li1.4Al0.4(Ge0.67Ti0.33)(1.6)(PO4)(3) treated at 950 degreesC for 18 h. Mechanisms for the enhancement of sigma(totle) in glass ceramics were given and discussed. The high conductivity, good chemically stability and easy fabrication of the Li1.4Al0.4(Ge1 - xTix)(1.6)(PO4)(3) system suggest that they are promising solid electrolytes for all-solid state Li ion rechargeable batteries. (C) 2004 Elsevier B.V. All rights reserved.