The increasing demand for a safe rechargeable battery with a high energy density per cell is driving a search for a novel solid electrolyte with a high Li+ or Na+ conductivity that is chemically stable in a working Li-ion or Na-ion battery. Li6ZnNb4O14 (LZNO) has been reported to exhibit a sigma(Li) > 10(-2) S cm(-1) at 250 degrees C, but to disproportionate into multiple phases on cooling from 850 degrees C to room-temperature. An investigation of the room-temperature Li-ion conductivity in a porous pellet of a multiphase product of a nominal LZNO composition is shown to have bulk sigma(Li) approximate to 3.3 x 10(-5) S cm(-1) at room-temperature that increases to 1.4 x 10(-4) S cm(-1) by 50 degrees C. Li-7 MAS NMR spectra were fitted to two Lorentzian lines, one of which showed a dramatic increase with increasing temperature. A test for water stability indicates that Li+ may move to the particle and grain surfaces to react with adsorbed water as occurs in the garnet Li+ conductors.