Lithium borohydride (LiBH4) is a candidate material for a solid electrolyte of all-solid-state lithium secondary batteries. In this study, the hydration behavior and influences of hydration on the ionic conductivity of LiBH4 were investigated. LiBH4 was found to become hydrated without decomposing; structural water can dehydrate at 55 degrees C and then rehydrate at around 35 degrees C. Hydrated LiBH4 has a high lithium-ion conductivity of 4.89 x 10(-4) S . cm(-1) at 45 degrees C. The temperature dependence of conductivity and motional narrowing of the Li-7 NMR spectra at around dehydration temperature suggest that the enhanced lithium-ion conductivity is attributed to the motion of structural water molecules. (C) 2015 Elsevier B.V. All rights reserved.