Solid electrolyte material and all solid lithium ion secondary battery

There are provided a solid electrolyte material having high density and ion conductivity, and an all solid lithium ion secondary battery using the solid electrolyte material. The solid electrolyte material has a garnet-related structure which has a chemical composition represented by Li7-x-yLa3Zr2-x-yTaxNbyO12 (0≤x≤0.8, 0.2≤y≤1, and 0.2≤x+y≤1) and relative density of 99% or greater, and belongs to a cubic system. The solid electrolyte material has lithium ion conductivity which is equal to or greater than 1.0×10−3 S/cm. The solid electrolyte material has a lattice constant a which satisfies 1.28 nm≤a≤1.30 nm, and has a lithium ion which occupies only two or more 96h sites in a crystal structure. The all solid lithium ion secondary battery includes a positive electrode, a negative electrode, and a solid electrolyte. The solid electrolyte includes the solid electrolyte material.