The new one-dimensional quaternary metal thiophosphate KNb2PS10 has been synthesized by using a eutectic mixture of KCl/LiC1 and structurally characterized. The structure of KNb2PS10 is closely related to that of Nb2PS10 and comprises infinite one-dimensional chains composed of NbS8 and PS4 polyhedra. These chains are separated from one another by K+ cations. A chain may be formulated as (1)(infinity)[Nb24+P5+(S-2(2-))(3)(S2-)(4)(-)].