The reaction of Li2S and P2S5 with Li-4[SnS4], a recently discovered, good Li+ ion conductor, yields Li10SnP2S12, the thiostannate analogue of the record holder Li10GeP2S12 and the second compound of this class of superionic conductors with very high values of 7 mS/cm for the grain conductivity and 4 mS/cm for the total conductivity at 27 degrees C. The replacement of Ge by Sn should reduce the raw material cost by a factor of similar to 3.