The quaternary thio-phosphate, Cs(0.49)NbPS(6), caesium hexa-thio-niobiophosphate(V), has been synthesized by the reactive halide flux method. The title compound is isotypic with Rb(0.46)TaPS(6) and is made up of a bicapped trigonal-biprismatic [Nb(2)S(12)] unit and a tetra-hedral [PS(4)] group. The [Nb(2)S(12)] units linked by the [PS(4)] tetra-hedra form infinite chains, yielding a three-dimensional network with rather large van der Waals gaps along the c axis in which the disordered Cs(+) ions reside. The electrons released by the Cs atoms are transferred to the pairwise niobium metal site and there are substantial inter-metallic Nb-Nb bonding inter-actions. This leads to a significant decrease of the inter-metallic distance in the title compound compared to that in TaPS(6). The classical charge balance of the title compound may be represented as [Cs(+)](0.49)[Nb(4.51+)][P(5+)][S(2-)](4)[S(2) (2-)].