The asymmetric unit of the title compound, {[Ce(C(3)H(2)O(4))Cl(H(2)O)(3)]·0.5H(2)O}(n), contains a Ce(3+) atom coordinated by a chloride anion, three water mol-ecules and a malonate ligand, and one water mol-ecule of crystallization with a factor of occupancy of 50%. The malonate ligand is bonded to three different symmetry-related metal atoms yielding a one-dimensional coordination polymer running parallel to the a axis. A supra-molecular network composed of strong and highly directional O-H⋯O and O-H⋯Cl hydrogen bonds ensures a close and effective packing of adjacent polymeric chains.