The hydrothermal synthesis, single-crystal structure, and some physical properties of (CN3H6)(2).(VO2)(3)(PO4)(HPO4), a new guanidinium vanadium(V) phosphate, are reported. This phase is built up from vertex-sharing layers of VO6 octahedra, which adopt the hexagonal tungsten oxide motif. These octahedral layers are capped by P-O and P-OH entities resulting in anionic layers of stoichiometry [(VO)(3)(PO4)(HPO4)](2-). Pairs of guanidinium cations are arrayed in the interlayer regions in a manner that suggests interactions may occur between these species. Crystal data consists of the following:. (CN3H6)(2).(VO2)(3)(PO4)(HPO4), monoclinic, C2/c (No. 15), a = 12.446(3) Angstrom, b = 7.287(2) Angstrom, c = 17.819(5) Angstrom, beta = 97.23(3)degrees, Z = 4.