The title compound, [Cd(C(2)H(3)O(3)P)(H(2)O)](n), was obtained from vinyl-phospho-nic acid and cadmium nitrate. The vinyl groups project into the inter-lamellar space and the structure is held together via van der Waals forces. The Cd(2+) ion is six-coordinate and the geometry is best described as distorted octa-hedral, with O-Cd-O angles falling within the range 61.72 (13)-101.82 (14)°. Five of the coordinated oxygen atoms originate from the phospho-nate group and the sixth from a bound water molecule. Cd-O distances lie between 2.220 (3) and 2.394 (2) Å. The water mol-ecule is hydrogen bonded to a phospho-nate oxygen atom.