There is an urgent need to develop solid electrolytes based on organic molecular crystals for application in energy devices. However, the quest for molecular crystals with high Li-ion conductivity is still in its infancy. In this study, the high Li-ion conductivity of a Li{N(SO2F)(2)}-(NCCH2CH2CN)(2) molecular crystal is reported. The crystal shows a Li-ion conductivity of 1 x 10(-4) S cm(-1) at 30 degrees C and 1 x 10(-5) S cm(-1) at -20 degrees C, with a low activation energy of 28 kJ mol(-1). The conductivity at 30 degrees C is one of the highest values attainable by molecular crystals, whereas that at -20 degrees C is approximately 2 orders of magnitude higher than previously reported values. Furthermore, the all-solid-state Li-battery fabricated using this solid electrolyte demonstrates stable cycling, thereby maintaining 90% of the initial capacity after 100 charge-discharge cycles. The finding of high Li-ion conductivity in molecular crystals paves the way for their application in all-solid-state Li-batteries.