A new V4+ phosphate, Cs2V3P4O17, has been synthesized and its structure was determined from single-crystal X-ray diffraction data. It crystallizes in the orthorhombic space group Pnma with a = 17.613(5), b = 7.328(2), c = 11.600(4)Å, V = 1497.1(8)Å3, Z = 4, R = 0.0272, Rw = 0.0261, G.O.F. = 1.37 for 1402 unique reflections with I > 3.0 σ(I). The structure contains tunnels where the Cs+ cations are located. The framework can be described as consisting of V2O10 units formed from one VO5 square pyramid and one distorted VO6 octahedron sharing a corner, and infinite chains of distorted VO6 octahedra sharing opposite corners, which are linked in three dimensions through the pyrophosphate groups.