Lithium-ion-conductive material

Provided is a lithium-ion-conductive material whereby it is possible to form a solid electrolyte provided with high lithium ion conductivity by a sintering temperature of 800 DEG C or lower. The problem addressed by the present invention is solved by a lithium-ion-conductive material containing, in terms of mol% on an oxide basis, 36.6-37.3% of a P2O5 component, 43.0-48.1% of a TiO2 component, 0.6-3.2% of an Al2O3 component, and 13.9-17.5% of a Li2O component, the mol% of the Al2O3 component being 0.3-3.0 mol% less than the mol% of the Al2O3 component calculated from the compositional formula Li1+xAlxTi2-xP3O12 (x = 0.05 to 0.4) derived from the composition of Ti and Li, the mol% of the P2O5 component being 0.2-2.0 mol% less than the mol% of the P2O5 component calculated from the compositional formula above, and the lithium-ion-conductive material including a crystal phase having a NASICON structure in a rhombohedral crystal system or a Li1+xAlxTi2-xP3O12 (x ≥ 0) crystal phase.