Solid-state electrolyte as a crucial component in all-solid-state batteries should have high Li-ion conductivity and good stability in air. Recently, a new solid Li-ion conductor LiTa2PO8(LTPO) with theoretical and experimental Li-ion conductivities of 35.3 and 0.25 mS/cm has been reported. Herein, we systematically investigate the ionic conductivity and chemical stability of the LTPO electrolytes sintered by conventional sintering (CS) and hot-pressing sintering (HP) methods. The effects of Li sources, sintering temperature, and the dwelling time are concerned. LTPO pellets using CH3COOLi center dot 2H(2)O as the Li source sintered by CS method have a room-temperature Li-ion conductivity of 1.86 x 10(-4)S/cm with an activation energy of 0.36 eV. A conductivity of 3.12 x 10(-4)S/cm with an activation energy of 0.32 eV is achieved by further HP sintering. Moreover, LTPO shows excellent chemical stabilities in air, aqueous solution, and organic solvent and shows a stable cycling performance in the symmetric Li/Li cells and the all-solid-state Li/LiFePO(4)batteries with the separation of a thin PEO membrane.