Hydride-ion conductors have attracted considerable interest due to their high ionic conductivity and potential applications in hydride-ion-conducting devices. This paper reports the high hydride-ion conductivity of perovskite-type SrLiH3. Both computational and experimental results showed that the smaller ionic radius of alkaline-earth metals ( AE ) in AELiH3, the lower the migration barrier and the higher the hydride-ion conductivity. The ionic conductivity was further improved by introducing hydrogen vacancies by replacing strontium with sodium, and Sr0.925Na0.075LiH2.925 showed the highest ionic conductivity (5.0 × 10–6 S cm–1) among the reported hydride-ion conductors, at room temperature. The crystal structure analysis based on neutron diffraction data revealed the structural features corresponding to hydride-ion diffusion: namely, the presence of vacancies and large displacements at the hydrogen sites. These results demonstrate that the employment of small cations at the A sites in perovskite-type hydrides with hydrogen vacancies can provide fast hydride-ion conductors.