The title compound, potassium diniobium vanadium phospho-rus deca-sulfide, KNb(1.75)V(0.25)PS(10), was obtained by reaction of the elements with a eutectic mixture of KCl/LiCl. It is isostructural with the quaternary KNb(2)PS(10), but the Nb sites are occupied by statistically disordered Nb (87.5%) and V (12.5%) atoms. The structure is composed of anionic (∞) (1)[M(2)PS(10)](-) chains (M = Nb/V) separated from each other by K(+) ions. The chain is composed of [MS(8)] distorted bicapped trigonal prisms and [PS(4)] tetra-hedra. There are no inter-chain bonding inter-actions. The crystal used for the X-ray analysis was a racemic twin.