a magneto - optical recording medium includes a magneto - optical layer , a reflection layer and an inorganic dielectric layer interposed therebetween . the dielectric layer is extremely thin so that it will exhibit almost no optical effect , thereby allowing a high cn ratio to be obtained . thermal conductivity of the dielectric layer is so low that the magneto - optical and reflection layers are thermally isolated from each other . that is , if refractive index of the dielectric layer is n , thickness of the dielectric layer is t , and the thermal conductivity of the dielectric layer is c - 1 ), then the thickness t is set within a range that satisfies the following equation : 5n - 4 ≦ t ≦. sup .- 0 . 4 where c ≦ 4j - 1 .