The elastic modulus, fracture toughness, ionic conductivity, Li and water stability of dense (similar to 97%) fine-grain (similar to 10 mu m) Li1.2Zr1.9Sr0.1(PO4)(3) (LZSP) consolidated by reactive hot-pressing was investigated. Low values of elastic modulus (252 and 40.9 GPa), fracture toughness (0.29 and 0.37 MPa-m(1/2)), total conductivity (2.1 x 10(-5) S/cm) at room temperature were exhibited as a result of the presence of microcracks formed during cooling from the hot-pressing temperature. The lattice conductivity of LZSP is 0.85 x 10(-4) S/cm with an activation energy for bulk conductivity of 0.29 eV. The results of Li/LZSP/Li cell impedance as a function of time and surface examination suggest that LZSP is not stable against metallic lithium. The results of the water stability test suggest that LZSP is a possible membrane for use in aqueous Li-Air cells. The results of this study reveal for the case of lithium zirconium phosphates are as follows: 1] a small grain size is required to prevent microcracking to avoid a reduction in total conductivity and mechanical properties and 2] even though they do not contain a transition metal cation they are not stable against Li at room temperature. Published by Elsevier B.V.