A polymeric heterometallic compound, {[Gd₂Zn₃(C₄H₄O₅)₆(H₂O)₆]·12H₂O}_n, comprising zinc(II) and gadolinium(III) cations bridged by carboxylate groups from oxydiacetate ligands, is presented. The Gd^III cations lie at sites with crystallographic 32 symmetry and display a tricapped trigonal-prism arrangement, which is defined by six carboxyl and three ether O atoms. The Zn^II cations lie at sites with imposed 2/m symmetry and are octahedrally coordinated by four carboxyl O atoms and two apical water ligands, which form strong intramolecular hydrogen bonds. Comparison is made with the previously reported isostructural homologous copper-gadolinium complex.