In the title ammonium polyoxometallate salt, (C(6)H(16)N)(4)[H(2)V(10)O(28)], the anion features O atoms engaged in μ(6)-, μ(3)- and μ(2)-bridging of adjacent V(V) atoms, confering an octa-hedral coordination at each of the twenty unique metal atoms. Two anions are linked by μ(3)- and μ(2)-bridged OH units across a center of inversion, forming a dimer which is linked to the cations by N-H⋯O hydrogen bonds. The cation is disordered over two positions in a 0.776 (4):0.224 (4) ratio in one of the two independent ion pairs in the asymmetric unit, and 0.627 (10):0.373 (10) in the other.