The NASICON-type Li1.5Al0.5Ge1.5(PO4)(3))(3) electrolytes were synthesized by a facile aqueous-based sol-gel process with alcohols free. Compared with the samples prepared by solid-state reaction, the modified sol-gel derived Li(1.5)A(10.5)Ge(1.5)(PO4)(3) electrolyte exhibited a rhombohedral crystal symmetry without impurity phase and higher ionic conduction behavior. After sintered at 850 degrees C for 5 h, the sol-gel specimen showed a total ionic conductivity of 3.1 x 10(-4) Sian at 30 degrees C and 1.0 x 10(-3) S/cm at 60 degrees C. In addition, the chemical and phase stability of the as-prepared Li(1.5)Al(0.5)Ge1,s(PO4)(3) with three types of cathode materials (i.e. LiNi0.8Co0.15,Al0.05O2 LiNi0.5Mn1.5O4 and Li3V2(PO4)(3)) was investigated in the temperature range of 500 to 700 degrees C. This work proposes a synthesis choice for Li1.5Al0.5Ge1.5(PO)(3), and also favors to the electrode identification for all-solid-state lithium secondary battery using NASICON-type electrolyte.